03 slt quad cab, 4.7L 133,000 miles on it.
Basic tuneup and changed all of the coil packs (had two go bad according to the error codes).
Recently started having a problem with what feels like the transmission is bouncing between gears from 40-50 mph. Almost like it's rapidly shifting back and forth (shudder). The idle is fine, can rev without any problems with the cylanders. Which is why I'm thinking the transmission because it only does it at those speeds. But, if I get on the gas like I'm passing, then it shifts and rides just fine. Just doing it during normal acceleration. Also, doesn't matter if I'm in OD or not. Either one will do it.
Did some searching around, but unfortunately couldn't really find much related to what I'm experiencing.
Oh, there aren't any error codes coming up either. Would make it a little easier to diagnose if there were lol
Any help is appreciated, since I'm trying to keep the truck alive (just had my first baby so we're trying to save as much money as possible at the moment).

 

Welcome to the forum.
You say basic tune up, what kind of spark plugs did you install?

 

Stock plugs, got them from the dealer when I picked up the coil packs. Honestly didn't even look at them and can't remember what they were labeled. It seems to idle fine, even stepping on the gas (in neutral) doesn't do anything other than take the rpm's up.
It is now slipping when going around corners. So I'm thinking the transmission. Could it be a sensor or am I looking at something much bigger? Oh, inspected the U-joints just to be on the safer side.
Appreciate the help, but I'm thinking that the trans is going to need some serious work. Wondering if it's time to just start looking at picking up a new truck. Just really didn't want to do that with today's economy. Alot nicer to avoid that monthly payment...

 

A trans rebuild will likely be $1500-2000 depending on your area. The 45RFE isn't a bad trans unlike the 46RE that came before it, so you can likely get off cheap by finding a trans on craigslist or in the junkyard.

And I fully understand the car payment thing, my rig is paid off and I love it. Parts are a small price to pay to keep the bank from picking up your ride.

 

Kinda figured it was going to be a rebuild job. But ya never know if you missed something trying to diagnose the problem, so always better to ask. Appreciate the info from you guys. The wife is pushing for a new truck, but i think that's because this one has stranded me 3 times in the last 6 months. So she's getting a little sick of that, not to mention if I would have had my 11 month old son with me. So if she has her way, I'll be ordering a new truck. Hoping that I can get this one fixed, but probably just use the money as a downpayment on a new one. If anybody else comes up with any options, I'd be glad to hear them. Love this forum, alot of great information to surf through. Was a member here before, but my old pc crashed and I lost my login info, so just created a new account.