Could use some help diagnosing...

2001 5.9 cummins 4X4 automatic transmission.

While driving with the air conditioning on, about once every other minute, it feels as if the transmission is slipping out of gear. I can feel a momentary loss of power, hear the engine rev a little higher, and watch the tac jump a little. Now, this has never happened when the air conditioning is not on which leads me to believe it is not that the transmission itself is not slipping but maybe there is a clutch on the AC compressor that is engaging and disengaging quickly?

Anybody heard of this or have any thoughts??

The truck is new to me and the AC doesnt blow cold, so I think it might have something to do with the compressor.

Any help is appreciated thanks

 

Does this by chance happen while cruising between 45-70 mph?

 

thanks for the reply.

I usually only pick up on it while cruising on the freeway or around 55.

Im pretty sure its happened in 3rd gear as well. I will play with it a little more tomorrow and see if its happening in all gears and all speeds.

 

What your describing sounds a lot like whats known as "converter lockup hunting".It is a well known and common issue with these trucks.Basically its an electrical issue that causes the torque converter to lock and unlock while cruising for no reason.It sounds like exactly what your describing,feels like trans is slipping out of gear for a split second,rpms go up a little,feels like less power.Do a search on google and you will find a lot of info about it.It usually boils down to being a bad alternator causing electrical noise in the toque converter clutch circuit.