Alright guys, I've just done most of the above. Here is how mine worked out....

The 33's with 3.55 did OK. Not a big notice unless towing something heavy.

Went to 35's with the 3.55 gears still in there. Drove a couple of years this way. Truck was a dog. No way to use overdrive unless I stayed over 75mph. Cruise the highway at 70-75 without O/D around 2800rpms. Tow a trailer to bike week on the highway at 2700-3000 rpm's. Real bad gas mileage. By the way the speedometer was off by 10% so mpg was a little better than originally thought. 300 miles devided by X gallons = Y. Add the 10%, 330 miles devided by the same X gallons = MORE Y.......

Finally I bit the bullit and spent the money on a set of 4.56 gears and had them installed. The truck runs it's *** off. Shifts like it has a serious shift kit. The O/D is usefull again. The 4.56 was a little more than needed for the 35's but I'm OK with that. On I95 going to work running with traffic around 70-75mph the RPM's are around 2300. I can get a more exact reference on the way home in the morning.
It would have been nice if someone had 4.30 gears. It used to be at 77mph the speedometer read 70mph. Now at 70mph the gauge is at 85. I guess I'll need to get bigger tires to compensate. All I needed was a good excuse to jack it up some more and really **** the wife off.

Our trans ratio is .69
How can I determine what ratio to use for my application?
mph x gear ratio x trans ratio x 336 รท Tire Diameter = RPM
Tire Diameter

Example:
70 mph x 3.73 (gear ratio) x .67 (trans ratio) x 336 รท 27(tire diameter) = 2176RPM


70 mph with a 3.73 ring and pinion over drive transmission in 4th gear with a 27" tire will perform at 2176 RPM

 

I really don't see what the complaint is from all of you about the truck being a dog. With my worn out transmission, 3.55s, and 34" tires with heavy 20" wheels, I have no major issues. Yes, it does bog down more at lights, but on the highway you see real savings. I raced using 31"s, then put the 34"s on - there was a .5 second difference in the ET (the 34"s made the truck .5 second slower) and the top speed was about a 10mph difference (the 34"s were faster.) I've noticed that the truck bogs slightly, but once it reaches about 1800rpm, it takes off and goes until it redlines. When driving at around 45mph in 2nd gear, a quick tap of the accelerator lifts the nose a nice 4-6"s.

Anyway, the other concern: I make around 16mpg average. Around 20 on the highway, and closer to 13 in town. I've heard many of you say that you don't use OD in town, but I do. Want a quick way to see what's more efficient? take note of how much pedal you are using in 3rd, then allow the overdrive to lock up and see if you don't pull you foot out a little to maintain the same speed.

Less pedal = less fuel being delivered = less fuel being consumed - hard to argue with that.

There is a 12% difference in speed over stock with the 34"s - in OD that means I can run 80mph at 2000rpm, instead of 73mph at the same rpm with the old tires. Now, sometimes it will bog down on long, steep hills, but for the most part, it acts just like it did before, but now I run at lower rpms.

Anyway, I've considerd going up a gear size or two, not because the 3.55s don't work well, but simply because I miss my .5 second! I considered going with a 3.96 Suregrip; maybe, maybe a 4.10. But a 4.56? Nah, that's just overkill for anyone who wants decent fuel milage out of their truck.

 

MAN id be ALL OVER THAT if i only had a little bit of money!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

 

Still available///. How about you get me that interior and I swap you the gears...lol

If it doesn't put you out too much (on that wrecked truck>>>>>>>