95 F150 6cyl transmission drags

Here's the problem. - Transmission seems to drag. In reverse it seems to not quite engage into gear. Pulls on the motor and torques a little, but won't budge the truck. Same thing happens when in lo-gear. Put it in drive and it will slowly start to move but it take some effort - pulls the motor down. Once under way seems to fade but drags when I let up on the gas.
When does it happen? - after driving a while - 25 miles - under the hot Texas sun, after or during trailor pull (nothing heavy 2500lbs), or up and down hills. I have to let it cool before I can reverse again. Takes about 10 minutes.
No one I have talked to has heard of this. Need truck for work - please help. Truck has 58K miles and the fluid looks like it needs to be changed. A little dark but no bad smell. I hope there is an inexpensive fix.

It sounds like a pressure problem, like the pump cannot supply enough fluid.

How many miles on it?

That sounds like somewhere to start. Sometimes if I feel it start to stick I can gas it as I'm shifting and it will lurch into gear. Explain to me if you will how the pump works and some problems you've encountered. I'm not very familiar with automatic transmissions. 58k original miles on the truck. I've only had it about 2 months and it doesn't appear to have been well maintained. It had original plugs, wires, fuel filter, cap, rotor, etc.

My sister has a 93 Lebaron that was somewhat doing the same thing. Put it in gear and it wanted to not go anywhere. Wouldn't go in reverse either. Her boyfriend at the time was an automotive mechanic. He took the car to the shop and changed the transmission fluid and it has worked fine ever since. That was about 5-6 years ago. Try changing the fluid and see if that helps any.

- cdawley1 - I plan on changing fluid, flushing and purging, changing filter as soon as I can. I hope you are right.

Could be a plugged filter causing a starvation of fluid, in turn a delay in power supplied to transmission