Bucking in OD

[06_6.6]

I'm having an issue in while I'm in od that causes the truck to 'buck' when holding or slightly accelerating. It feels like my dshaft is about to fall off. Last check of my rear ujoints they were fine but I'll check again. Could this be tc related? Truck is an ex cab short bed 4x4 380100 miles

Sent from the land of teepee's and buffaloes

 

[Mike L.]

Any codes? Check engine light on?

 

[06_6.6]

I have a cel for glowplugs. Unable to read transmission codes unfortunately. Fuel filter needs changed as well as the Allison spin on. Trans temp is 125

Sent from the land of teepee's and buffaloes

 

[btfarm]

In 2 or 4 wd ? All tires the same diameter and pressure?

 

[06_6.6]

2wd, 285/75/16 65psi front 55psi rear.

Edit: I just went out and pulled codes and it shows a P0128

Sent from the land of teepee's and buffaloes

 

[The Neens]

Edit: I just went out and pulled codes and it shows a P0128

Probably have a bad thermostat, replace both...