2500 hops in 1st gear

[JCarreon]

I just bought a 2003 GMC Sierra 2500 with 58000 miles on a 6.6, Allison, 4X4, lifted, 35"tires, long bed, and a quad cab. It has an Edge computer progammer and big exhaust on it. I got it in Wyoming and drove it to Las Vegas. It did great and got 15.5 mpg with going through the Rockies. The problem I am having is that when I accelerate from a stop, the truck shutters and hops till it changes gears. I havent had a chance to look closely at it yet. It feels as if a band is too lose in the trans or something. I have no experience on these transmissions. My buddy has the same truck and says his does the same thing. Looking for some advice on what it could be? I have another problem with the tranny not going into park, but I'll be asking about that later. Thanks.

[rapidoxidationman]

Are you sure the shift linkage is properly adjusted? Might be what's stopping you from going into park (hopefully).

What color is the transmission fluid? When was it last drained/filled? Is there enough in the pan? Is there too much in the pan? Any diagnostic codes? (You can buy an OBD-II reader for about $80)

[Edahall]

I just bought a 2003 GMC Sierra 2500 with 58000 miles on a 6.6, Allison, 4X4, lifted, 35"tires, long bed, and a quad cab. It has an Edge computer progammer and big exhaust on it. I got it in Wyoming and drove it to Las Vegas. It did great and got 15.5 mpg with going through the Rockies. The problem I am having is that when I accelerate from a stop, the truck shutters and hops till it changes gears. I havent had a chance to look closely at it yet. It feels as if a band is too lose in the trans or something. I have no experience on these transmissions. My buddy has the same truck and says his does the same thing. Looking for some advice on what it could be? I have another problem with the tranny not going into park, but I'll be asking about that later. Thanks.

Sounds like the classic axle wrap due to a lift that was set up improperly. You might want to check your drive line angles with respect to the axle tilt.

[JCarreon]

I have not done or checked any of those things as of yet. I was told the guy whom owned the truck had a "shift kit" installed. As a result, to park the truck, I have to put the truck in reverse and set the E- brake to get the key out. The shifter goes into park, however, the trans doesn't. To start it, I must put the truck into neutral. Being that neutral lines up with the shift indicator and the transmission, I didn't think an adjustment of the linkage was the fix. I was told that if I physically put the linkage into park, it will get stuck and require work to get it out of park.

[cowboywildbill]

Just a guess, maybe it might have screwed up the nsbu when he worked on it. There is a tab or clip that keeps the switch in the correct position in relation to the shaft when installing it. Or he may have messed up on the detent inside. I would have an allison dealer look at it.

[cowboywildbill]

PS Sorry I wanted to add more but was too late to edit my previous post.
It could be more than one issue as mentioned before, like axle wrap and maybe even a bad shift cable also?? I wouldn't run it until I knew what was really going on. I'm guessing the shaft /detent isn't lined up in the valve body or something wrong along those lines or NSBU might be miss aligned. Good Luck and
Let us know what you find out.

[JCarreon]

Thanks for the input. Any of what you said could be possible. I will get it all checked out and report on the findings.

[Kennedy]

With a crew cab long bed you have a 2 pc drive shaft. The angles on this setup can be pretty tricky to get set up properly on a std height truck let alone lifted. Also check the universal joint right at the transfer case.

Lift kits are cool and fun and all, but sooner or later people get sick of them and end up taking them out only to rejoice at how much beter the truck handles and how the MPG improves.

On the shifter it sounds like it is seriously out of adjustment. There should be no reason that Park does not function.


Secure the vehicle so that it cannot roll and take the cable off (it just pops off easily) of teh shift lever. Work the lever manually to the full forward position. Carefully release your brake/wheel chocks and see if you now have Park.


I believe the answer in the end will be that you need to lift the locking "C" from the cable while in Park and move teh linkage to true park and then lock down. It['s been a long time since I have adjusted one of these, but I think my description will be accurate.

I would definitely check what sort of "shift kit" was installed and by whom. If this aint right, I doubt the rest is either...