I'm having a issue with my transmission on a 2004 venture, when it gets up to normal operating temperatures. Whwn the van shift from first to second and then from second to third, there tends be a clunk or hard shift. This has just started in the last few weeks.

The problem is probably a bad Electronic Pressure Solenoid (EPC). Have the computer scanned at a dealership or a transmission shop to verify this. The code will probably be a P1811. The P1811 code sets because the transmission takes longer than 0.65 seconds to shift, then the computer commands maximum line pressure to make the car shift as fast as possible to avoid burning the clutches. Replacing the EPC is an expensive job, however, you can install a shift kit to speed up the shifting, and probably fix the problem. The shift kit is available from a company called TransGo. If you go to www.transgo.com you can look up a distributor in your area. The kit you will need is the SK®4T65E. Installing the shift kit is pretty easy for the 'shade tree mechanic'; if you can change your own transmission fluid, you can most likely install this kit yourself.