So I was driving up a local mountain elevation total of 5,000 ft I was at relatively the beginning of this mountain a little bit of history about my Jimmy, it has just over 200,000 miles I'm not sure about the previous owner and how well he kept up this truck but for me it has been running beautifully until I serviced the transmission a week before this issue.. which everything was still fine until I put on a set of all terrains , when I left from the tire center I noticed right away that the new tires were rubbing and that they put extra pressure on the transmission I'm thinking that the torque converter was completely stressed by the addition of maybe a quarter of an inch of tire. Fast forward to 3 days after the tires were put on I'm going up this mountain and got on the gas to increase my speed and I watch the tachometer go all the way up and come right back down which I'd never seen happen in a vehicle I was driving until this moment. it still kept pressure over the rest of the whole mountain and when I got to the other side and down to an inspection station I had to stop to tell the gal that I had no fruits or plants and then as I started to accelerate it slowly left me I could pull over stop the car turn off the engine turn it back on and barely get it to grab a gear and then nothing... Upon checking the transmission fluid it's still full whereas I thought that it must have all leaked out so I parked the truck had somebody come pick me up and just went and bought my mustang and had the truck towed back over the mountain two days later haven't done anything to it since but this morning got underneath it to see if a line had came loose or something and I can't see anything.. help maybe?? I can't afford to take it into the shop and between my willingness and limited amount of experience and my buddies extreme amount of experience I think we can get it done

 

If I had to guess, I would say the transmission filter wasn't properly installed when you did the service, or the fluid level is low. Did you check the fluid with the engine running and the transmission in park (or neutral, or whatever it says on the dipstick)?