Been watching, it indeed sounds like you had it on the wrong side. Are you sure you didn't leave out any washers, spacers, got all 6 thrust ball bearings in place?
also how tight does the differential have to be
Tighten it down tight, but not enough to break it, then back off 1/8-1/4 turn. This is very important. I usually do little "wiggles" as I tighten it back and forth until I can feel it's as tight as it will go without breaking the bolt or slipping off, rotating it by the other wheel in between each time to make sure it's seated. Now back off 1/8 turn. If this is not right, the balls will slip on the diff rings and dig a groove, frying the diff rings. They are supposed to ROLL on the rings, not slip. In extreme cases it can melt the diff gear, which is a GOOD REASON to use some slipper clutch! I use 1/8 turn back-off.
By the way next time you open the case, try flippng the diff rings over, it's almost like having new ones. You're supposed to put the side with the curved edge toward the balls, but if the rings have a groove, flip 'em over.
Team Associated. I gave you the link to the page because there's several, part 1 and 2 and parts lists.
So when i get it put together, if it pulls left or right what do i do, except make sure the rims are evenly tight and the steering is straght. Do i loosen or tighen the diff bolt depending on which way it pulls.
You don't do JACK to the diff. Leave it at that setting above. First, turn on your electronics and center the steering trim, and give it a good push on level concrete. If it doesn't roll straight, adjust the steering by the turnbuckles and servo control arm until it does. Wiggle the front wheels. If they swing more than 1/8" in either direction, you have some slop in the front end you need to sort out.
Now that the front end's right, it's normal for it to pull **A LITTLE** to one side on hard acceleration, especially with a big engine, but it should level out wthin a few feet. If it doesn't, you have something binding. Usually this is from leaving out the cone washers (SEE MANUAL) at the wheels, these are to keep the wheel against the bearings. There should be no binding on either side.
If it gets a little sideways on hard accel. from a dead stop, try loosening the slipper clutch just a little. This will help.