2doorfury

iTrader: (12)

Went from factory size tire to 15 inch wheel with 295/65/15. Shift thru all gears fine cruising and at WOT. Did a WOT pull and never went into overdrive. Now when cruising, it'll go into ovedrive until about 60mph, then down shift. Under WOT, it won't go into overdrive. It'll go to 90mph and hit rev limiter..anyone have any ideas?? I didn't think tire size would effect how it shifts, just shift points.

2doorfury

iTrader: (12)

Also, it seemed like this only happened when the trans. Was warm. Between 120-140. It never got above 140 tho.

03sierraslt

iTrader: (22)

I dont know what gears you have but you shouldn't be going into OD at Wideopen at 90mph anyway. Do you mean 3rd gear? Your above listed tire size works out to a 30.1", what was your factory size? Was the tune changed for the change in tire size? Tire size can change how it shifts, if you MPH limit is now not achieved then you can hit the rev limiter before the computer gets both inputs. The computer looks for both a RPM and MPH before commanding the shift, if it doesnt see both requirements based on what is set in the tune then it will not command a shift.

2doorfury

iTrader: (12)

I have 4.56 gears. Maybe it is 3rd gear I'm not going into. It hits around 90 and its out of gear. It was tuned with factory tires, which are a 245/75/16 I believe.iit

2doorfury

iTrader: (12)

When normal driving, it'll stay in OD until about 60, then either unlock or down shift. I'm kinda lost right now as to what's going on. Maybe I'll put the factory tires back on and see what happens.

03sierraslt

iTrader: (22)

Not sure what your limiter is set at but there is a minimal difference between those two sizes, however it could be just enough to cause a issue depending on how the tune is set. I dont know how loose your stall is but here are some rough numbers for when it should be shifting.

39.8 1st
74.7 2nd
121.8 3rd
174.0 4th

All shifting at 6200rpm


This is why I am not sure what is up with having issues at 90, unless your speedometer and tire size already in the tune are not right.

PaulyC

Are you sure that its actually shifting and not the converter locking and unlocking? When it downshifts at 60 whats the rpm jump?

2doorfury

iTrader: (12)

Stall is 3600 and limiter is set at 6500. Tuner adjusted speedo for gears and tire size. Truck was fine before tire and wheel swap. And there is a minimal tire size difference which has Mr stumped. It shouldn't change it enough to mess with how it shift or acts up.

2doorfury

iTrader: (12)

I'm not too sure if its down shifting. I'm guessing its unlocking. Rpms only jump maybe 300-500

PaulyC

I meant the engine rpm. If its less than a 2000 rpm jump at 60 it sounds like your converter is just unlocking.

edit- saw your other post. if its only a few hundred the trans isnt shifting its the converter.