Truck has been slipping on the high way when I hit the gas and it just revs. Let off and hit it and boom takes off like a rocket, now it's slipping at 20 miles per hr, give it more gas it just revs up, pull over put it in park. Then take off slow , then it's ok then when doing 40 it starts to just rev, check relays , wires, air leaks , have no engine lights on. Fluid is good and smells good. Was told try out put speed sensor on back of driver side trans, not a speed sensor that they gave me. Trying simple things before I have to drop pan, had 5 surgeries in two years. Would output speed sensor have anything to do with trans slipping? Speed sensor I read has nothing to do with the issue?

 

Try removing the main transmission harness. It's about halfway back in the transmission, drivers side. Now, test drive it, but you will only have 3 gears, 1,2 and D, and have to shift through manually. No automatic function.

If it continues to slip, time for a rebuild. If it works great, needs new electronics in the transmission.

Or you could try a bottle of Lucas transmission fix.
And make sure your checking the fluid when it's hot, and it's not too high, or too low.

 

Sounds like you should try a new trans filter.