4l65 off a Silverado ss. I cannot get this thing to shift when the computer tells it to. When logging the shift commands at part throttle I can see that the computer is sending the shift command, but the shift does not start to happen for several seconds. At WOT it will stick on the rev limiter until I let off the throttle.

The log shows that the computer is telling it sometimes to shift to third and even fourth before the 1-2 actually happens. With the engine off I can command the shift solenoids and hear all of them clicking so there doesn't seem to be a communication issue. Is this a pressure issue?

 

I have not heard of these exact symptoms. Yes, I would start with a line pressure check as very low pressure could cause significant shifting delays as well as trans-destroying slippage.

 

Going to check line pressure later, might not have a chance until the weekend but Im not driving it anyway.

The trans was sitting around for potentially months, it came from a parted out truck and supposedly worked well before. If there are parts sticking in the valvebody from dried out fluid having been in there, how do you get them unstuck?

 

Trans fluid does not dry out, it is mostly hydraulic oil. A trans can sit for years and still work perfectly as long as you let it warm up gradually. The main thing that will gum up a trans is friction material and by the time there is enough to clog up valves you need a rebuild anyway.

 

According to my pressure gauge, pressure seems low at idle and in gear, but builds sufficiently. Idle is around 50 lbs, reverse sits at 65 lbs. Putting it in reverse or drive and holding the brake while pushing the gas it hits over 100 at very light throttle, and it goes over 200 before the brakes have any trouble holding it.

 

At about 220 psi the gauge would start going crazy. It may have been partly the gauge, but the line did also feel like it was pulsing. It was a very consistent pulse.