I have an automatic 4 speed transmission. Right now my car is not
switiching into fouth gear. It also jumps up and down from 2 and 3
almost randomly. I can rev the engine upto 40k rpm and it will not
switch... However, occasionally  if I rev it up to like 50,000 rpm and
lay off the accelerator it wil slip into 4th gear...

This problem happened on a wet rainy day while I was on the highway.
Before this problem the transmission would slip or jump about 5k rpm
before it went into 3rd gear... It still jumps like this now...

I am basically trying to figure out whats wrong with my car. I have had
transmission problems with this car for the last 6 years... This will
be the third transmission and also third switch...

I think it may be either...

1. The computer? When the car gets wet maybe the moisture builds up in
the computer and the switch does not get nfo from the computer. Same
problems last year when it was cold and wet... So I got the
transmission and switch changed... Problem resolved except for the gear
slipping a bit...

2. The switch. Maybe it's defective. This is the third switch and it is
8 months old. (could have installed a used switch) I think gears 1-2-3
are hydraulic and for the tranny to switch into 4th the switch needs to
electronically signal the transmission?

3. The transmission. Maybe its broke... Like I said it slipped into 3rd
gear and maybe its just finally failing.

4. My theory is that the transmission problems started when some
numnuts changed the radio in the car. The electronics have been funny
ever since and the electronics may be burning out the switches or the
computer.

If you have any ideas please help. With the money I have spent on this
car, I feel like I could been driving a new S4 with the sports
package... and the 20 inch rimms like Mike Jones...

-Jakub