Alright so I have a 300 miles journey coming up in a couple days, and I will of course be doing a lot of highway driving. Now a quick few concerns about this trip. I have 33.5 inch tall tires with stock 3.55 gears. Now ideal speed for this trip would be around 65 mph give or take a few. Now I will have maybe 200-300 pounds of gear in the bed and 2 passengers total for this trip.

Now I'm not sure if I should keep my O/D off or on during most of the trip. When I'm in overdrive and have that setup, my truck is a dog, lacks power and struggles to get up hills. But when I have my O/D off my truck has great power but the rpms are a little high for my liking, there's no happy medium. I'm not sure if this is a good rpm to cruise at, I'm at just about 2350-2400 rpm at about 64mph. Now is it a good idea to keep that rpm for a 250 miles highway drive? I'm not towing, or have too much weight in the truck but I am running almost 34 inch BFG All Terrain Tires. I'm not so much worried about fuel consumption although it helps, but is it a bad idea to keep my engine at such rpm for that long of a time? Or would it be worse if I kept in O/D and have it struggle at about 1600rpm?
Wind is a big factor as well. I notice that the slighest wind slows me down the most, its like pushing a brick through the air.

Another question as to my O/D off switch, I was also thinking of just turning it on and off. I will be traveling in the mountains of Vermont so power is necessary. Is it a bad idea to turn O/D off at speeds of about 60mph? I'm not worried about the rpm spike as much as wear and tear on the transmission? i figure its probably the same as downshifting but would just like to be positive. Thank you very much for all input.

 

Leave it on when the road conditions permit, turn it off when they don't. You aren't going to hurt anything by doing so.

What you really need though, is to re-gear the axles. 4.10 would be good, but, you might like 4.56 better for driving around the mountains.

 

Okay, I was not sure as to if there was or recommended speed limit as to turning it on and off as the 4WD.
That's the exact next project, I'm on the fence about 4.56 or 4.10. I won't be doing much "mountainous" driving in the future just occasional twice a year trips from Long Island to New Hampshire, but will be doing a lot of highway driving for the next 3 years as I'm at college. I don't do a lot of towing and if I do its a 1958 16 foot custom craft boat, I can't imagine it weighs more than 2000lbs. 4.56 would be GREAT power wise, but I'm thinking may be a little too radical for my day to day requirements. But there is also the thought of bigger tires in the far future but that's very distant. lol

On a side note, I think I'll take your advice, when I see a big hill coming up, I'll just turn that O/D off and I'll sail up to the top and turn the O/D back on.
Thank you.

 

I have 4.10s from factory (off road edition) and I run 285/70/17 toyo AT tires...my truck does just fine on all hills here in western PA...if I were towing anything, I turn OD off but otherwise I just let it roll...your tires are a little bigger than mine, but i still think the 4.10s would be better for you. I've heard some people even say that the 4.10s will do ok with 35s as long as you aren't towing.

 

I remember reading on another forum, or maybe I used an online gear calculator, where I compared the final drive ratio with stock tire size (245/75/16 or 30.5in) and 3.55 gears to running (295/75/16 or 33.5in) and 4.10 gears and the final drive ratio on the bigger tires was actually lower. Don't quote me on it, but I'm pretty sure that's what I read. Now that sounds perfect for normal driving, back to stock specs, and a little lower drive ratio will give that little extra "oomf" needed to turn those larger tires. Hopefully lower gears with a Sonnax Sure Cure kit will be the next project.

 

The sonnax kit is def a nice addition....make sure you get rid of that pesky check valve in the tranny line by the radiator too! I did a little valve body work to my trans as well (just swapped some valves that allows fluid flow to the trans when in park and operates as a check valve in place of the in-line one)...will be installing the beefier borg-warner solenoids next time my pan is off.

 

Ahh I almost forgot about that pesky little valve. That's definitely on the list of things to do. In a couple weeks I'd like to do that Sonnax kit, delete that check valve, and change the fluid/filter. I have no problems with the tranny, but I'm sure it can't hurt. Hopefully some new gears would wake this thing up also.

Any idea on how much that Sonnax kit cost?

 

Woops, just found it for $112.87

http://www.transmissionpartsusa.com/...-sc4647rhe.htm

 

You guys are all upgrading your auto to keep it alive and im just wanting mine to die already so i can justify the money to put a NV4500 in lol

As far as gears, I have 4.10s with 265/75/16 now. Which is definetly lower then stock ratio with the 3.55. I drive in the mountains all the time. And i am getting better mpg now then i ever did with 3.55 ratio.

I am in the habit of cutting od off as soon as i get the truck and then only cutting it on when I get to long flat road or something more conducive for O/D

 

Ah those gears must be so nice, that'd be ideal. I want mine to die so I have an excuse to drop a nv4500 in it, but my wallet doesn't, lol. Hopefully in the near future shell get some nice 4.10 gears.

I think I might be turning it on and off a lot during this trip, lol.
I'll tell ya though, its so nice when its off, power is right there when ya want it, I want that nv4500 so bad.