Transmission not shifting at high gear.

Does it cut out at 3000 rpm in ANY gear, or just at highway cruise in high gear? I ask this because what can happen is that if you spend a lot of time cruising at one speed (long-distance commuter, over-the-road driver), what can happen is the the TPS (throttle position sensor) will get a dead spot on it from excessive wear. This will cause bucking, drop-offs, a stuttering whenever you happen to hit the dead spot. Typically, timing or ignition-type problems are not going to be rpm dependent, although they may be felt more prevalently a certain speeds/rpms. Transmission issues usually occur at shift points, and not at cruise speeds.

Check transmission solenoids. Lucky I have a spare trans to swap solenoids and fixed the problem

Go to auto zone to check for code it is fee.

Throtle position motor faulty

First I need to ask is it a 4 speed or a 3 speed transmission. If it's a 4 speed when driving down the road pull it from drive to third gear. You shpuld hear the engine speed up if it does not then that means you have on 4th gear and you will have to take it to a transmission shop. If it's a 3 speed then just count the shift points if all 3 gears are present then drive down the road and see if the van goes into tcc. When you mean the rpms are high how high are they.

take it to cottman transmission

It sounds like the last gear in your transmission may not be engaging. Caravans are actually famous for tranny problems. Furthermore, be sure to check your transmission fluid while your vehicle is idling. That ensures accuracy. But you may have to get someone to physically look at it to ensure your problem gets solved. Kind of risky diagnosing something so big through typing.

That is normal,If you do the same speed in 4th gear the rpm's will almost double.

The rpm's will repond faster in a manual than an automatic.

In a manual the engine supplies the power required directly to the gear that you have selected thus the engine rpm's will increase or decrease as needed.

have the transmission checked out,

quote http://www.aa1car.com/library/2002/bf90222.htm

One of the most common complaints with automatics is fluid leaks. Fluid can leak out of the driveshaft seals, the input shaft seal, the transmission pan gasket, the torque converter or the ATF cooler and line connections. If the fluid level gets low, the transmission may be slow to engage when it is shifted into drive. Gear shifts may be sloppy or delayed, or the transmission may slip between shifts

These cars have a lock up torque converter meaning 4 gear going above 35 to 40 MPH, the engine and transmission lock together and turn at the same rate. I know that older GM cars had a plug that needed to be plugged into the transmission for the lock function to work on the torque converter and if you unplugged it the RPM's would run high as you describe. I have never had a 1999 Silhouette and I'm not 100% sure that these cars have that type of plug but it sounds like that type of problem. I agree with you. You know your car and I would take it to a transmission mechanic and describe your problem to them.

Good luck!