Alright I have a 99 silverado z71 with the 5.3. I think it has the 4L60e transmission and 203000 on her. I am going to try and give as many details to see if yall can help me.

It will not do it in any other gear except when it hits over drive. When I am driving and reach about 40-45 mph it goes into overdrive and does an almost pulsing action. It stops once i get to about 56-60 mph. This pulsing thing i am talking about is that has a rhythm to it, never gets faster or slower and the rpms fluctuate about 200 rpms.

It think I can barely feel like its not fully engaging when it fluctuating like it does. The only other way to describe it as if I were driving a standard and while driving I was pushing the clutch just enough to where the rpms go up a little bit and letting the clutch back out.

Also if I put my truck in tow haul mode it does not do it at those speeds or at all. So it only does it between 40-55 mph under regular driving conditions and does not do while accelerating, only when im driving at steady 40-55 mph. It will accelerate no problem, but when I back off to cruise it will do it.

Is this my torque converter wanting to keep engaging and disengaging, and I need to buy a new one OR since it only does it in overdrive is there a sensor or something I can replace to make it stop doing this. I appreciate any information you guys can give me I really want to get this fixed so I don't ruin my trans.

 

Sound like the trans is slipping in overdrive. Based on the mileage it is very likely. The only way to know for sure is to scan the trans computer and perform a line pressure test.

 

So Im basically gonna have to take it somewhere to get it checked out?

 

Clear the codes, duplicate the symptom and then read the codes again. If the problem is in the transmission, it will set a code.

If not, you have driveability issues.

Allan

 

Okay I will do that thanks yall, just for kicks do any of yall know if the 6.0 trans will fit the 5.3 with housing and electric wiring and what not. Also, do any of yall know how much a new trans for my truck would be from chevy.