Truck kickin my stuff

[Core250PSD]

Forgive me, this will be long winded. So I was driving my truck (97' Ford F250 PSD automatic transmission 4X4) for a drive up to parents when I started pulling a slight grade and so I gave it some throttle and my RPM jumped up to like 3K or so, and I wasn't gaining any speed. It was actually decellarating. So I immediatly thought REMOVED BY ADMIN it's my fuel filter. So I alway keep a spare I changed it right away...that wasn't the problem. So then I figured it was my transmission slipping. I took it to AAmco and had them do a free test drive, and they said my tranny was fine, it was my engine that was the problem, so I told him he was aRemoved by Admin and wanted a second opinion, so I went to a little local tranny shop, he ran the scanner/tester on the electrical things and said it wasn't throwing any codes. So he took it for the spin and said it wasn't the tranny, it was probley the TPS(throttle position sensor) So he double checked that, and turns out it was fine. So he said take it to a auto mechanic. I took it to a international garage, and they ran the code reader/tester on it as well, said there was nothing wrong with the motor, it was the transmission. So again I go to ANOTHER transmission shop, he says theres nothng wrong with it. I'm stuck with a truck thats jacked up and apparently nothings wrong with it!!! Yet this problem is occuring more frequently now, sometimes 3-5 times a day. HELP!!