HUGE tranny problem! HELP!!

Hey all! I'm new, and need help!
I have a '96 F150 ex cab. Approx 120,000 miles on her. It has the heavier tranny(can't remember which at the moment) from the factory. The tranny is an overdrive tranny as well. She has been well maintained.

She is my daily driver, so need advise asap!

Here is the problem: early in the summer she started to vibrate in the frone end. We(my Huband and I) thought it was uneven tire wear at first. She had a pretty worn set of boggers on her. so, we changed the tires. The vibration didn't go away. It got so bad sometimes, we had to stop the truck. Lo and behold the U Joint was toast. We replaced it. Vibration gone..But...
Now, she bogs down badly. She either shifts too late, or not at all. The RPMs are all jacked, about 4,000, sometimes when she shifts. Some days it doesn't act up at all, others, it does it all day. I'm thinking its the torque converter. Everything was fine until the vibration from the U joint, so I was thinking since its all connected, maybe the bad vibration jacked the torque converter....

Any ideas??

Sucks for you by being so erratic. The problem is either electrical, or a sticky valve. First look at is that all electrical wiring is securely connected, clean, and not frayed or anything.
If there are not problems there, change the fuild and while there you guys could drop the valve body and see if its dirty. No matter what anyone tells you, do not flush it now. It is almost 20 years old and has 120000 miles. The problem is that flushing stirs contaminants up that should stay in the bottom of the pan. Those contaminants go throughout the tranny and that's bad...
Changing the fluid just gets rid of them, not clears them up. I don't remember if it has a drain or not, but if it does drain the tourqe converter too.

Id check the fuel pump, i had the same kinda prob with my truck... at first i thought it would only run good on rainy days, lol... but after a while it just got worse and then it just didnt run, it would turn over but wouldnt start. Took it to the shop and it was the fuel pump. just a thought...

There are a bunch of factors that can cause these problems with the trans. If you want to go the cheap route before getting into a costly rebuild. I would try for an MLP switch/Trans Range Selector/Neutral Safety switch. They are known by many names, but the general location is on the side of the transmission where the gear selector comes out of. If that stupid little thing is out of sync the vehicle would be hard to start or will shift erratically. Also, check your TPS (Throttle Position Sensor). That helps control the air/fuel mixture and again can cause erratic shifts.