I've only had my 2002 GMC dmax for a couple of weeks. As far as I know everything is stock. I went to pass a truck today and the tranny downshifted, the motor reved out to like 3k and wouldn't upshift. I was stuck next to the guy I was trying to pass (truck wouldn't go above 60mph). I could get is to upshift by letting off the throttle. Is this normal? Also from a stop, If I just floor it, It feels like it won't shift out of 2nd or 3rd until I let off the throttle briefly. When I had a F250 powerstroke I don't remember the tranny not wanting to shift under full power.

When was the last time the spin on filter was changed? I've heard this symptom posted here before and the reply from other members was "change the spin on filter". Let us know if this cures your problem.

I'm interested in all answers on this question also. My experience is when towing a 5er, approx. 9,000 lbs on flat land, the trans. doesn't want to shift out of 4th into OD. Normally I can let off the pedal about 62mph and it will shift, but then other times it just doesn't want to and refuses to shift. I'm stumped. I changed trans. fluid & inner filter at 25K mi, change spin-on filter every 5K mi.
'03, DA, ext.cab, 4x4, 64K miles. F&R axle fluids changed at 25K.
Any ideas will be appreciated.

does anyone have any idea why my tranny won't upshift under full throttle acceleration? I'm still having the prolem.

I have the same problem as KAISERRW has anyone answered your problem.

If I recall correctly, I think changing the fuel filter should solve your problem. Ask Kennedy about it, I am pretty sure he is the one who recommended the fuel filter change to solve the problem. Odd I know, but apparanty it fixes it.

KAISERRW & wschexnaydre: Sounds like you may be getting into shift stabilization. Before the transmission will upshift it will look at the throttle and the torque needed to maintain speed. If it doesn't think it can produce enough torque in overdrive to maintain that speed at that level of throttle it won't upshift. This is to get rid of the annoying 5-4-5 shift business when towing on rolling hills.

fool32696: I'm wondering if your engine isn't producing full power. Is it getting up to 3600 RPM at full throttle? Like I stated above, if the transmission doesn't think it can maintain speed in overdrive it won't upshift.

Also, you may want to see if your transmission computer has the latest software. There was a service release for the 2002 model year that may help.

Fuel filter neglect can often lead to this. Since the truck is new (to you) I'd suggest getting acquainted with it and changing all fluids and filter so that you know what you have and where you stand.

:exactly: Change the fuel filter

Can someone explain to me why changing the fuel filter will cause this?

Thanks, I Will Change The Fuel Filter And Go From There. I Had The Transmission Reprogramed About 2 Weeks Ago,i Find It Shifts Better In The Tow Haul Mode It's Just That Last Gear I Would Like To Get Without Having To Go 62 Mph To Get.

Can someone explain to me why changing the fuel filter will cause this?

When the fuel filter is restricted, you have to depress throttle further to attain the same speed. Depressing the throttle further tells the TCM you are demanding more torque, but you're not, so you are fooling the TCM with incorrect throttle angle compared to the speed you are actually going. The TCM will cause a later shift because of that throttle angle. Remember this is fly by wire.
Hope this helps.
mike

Thanks Mike. That makes sense I guess.

Machinater,
Thanks for the info. Just so everyone interested knows, I change my Tran spin-on filter every 5K miles, Tran fluid every 25K miles, fuel filter(s) every 15K miles. The last time my tran would not upshift I was on level ground, 60-65mph, with all new filters. 90% of my mileage is Interstate at 70mph.
I was hoping the Allison would think faster than me because I need all the help I can get ! The electrons in my jump box on top of my shoulders don't move like the used to !!

changed fuel filter today and truck now shifts fine.

thanks

Also thought that I should mention that it probably hasn't been changed in a long time. The sensor in the bottom came out covered in flakes of rust. Dumped out a lot of rust from the filter too.