Help please
 

I have a 04 screw fx4 with 175k miles on the chassis. The motor was completely redone with receipt for close to $10,000 and has about 30k miles on it. The transmission as far as the records go(which are extremely thorough) is original. The previous owner had the tranny and everything else flushed annually.

Now for the issue. I've had the truck 6 months or so. I lifted it slightly, put on 35x12.5 nitto's and immediately installed an edge evo tuner. When I'm cruising on the highway and I get to an uphill grade the truck will jerk forward quickly like something is locking up and then release immediately and continue driving. Sometimes it will do it a few times in a row and sometimes not at all. I can get the truck to do it in third gear as well. It's much worse when towing a trailer.

I've scanned it when stationary and nothing. I did a live monitor and could get it to produce a u1900 code but seems unrelated as that's an ignition communication error.

I don't want to just have the transmission rebuilt without knowing what the problem is. Hoping someone else has had similar problem or can help

Thanks

Had the same issue. Mine stopped after I put new plugs and coils in.