Going by your explanation, I'd look towards the Tx/Rx first. Possibly trims or something with the stick. If you are using a programmeable TX, make sure there's no mix or expo set. Also, make sure the turret is rotating smoothly and you don't have wires binding.

The rotation is just a simple motor/gearbox, it won't go in the wrong direction unless it's getting power in that direction. I have many Tamiyas and the Tiger I is hands down the best engineered of the lot. No need for upgrading anything on it, mine is all original and still running perfectly after 12 years with my kids driving it.

The only rotation mod that I'd suggest (and only if you find it an issue) is to glue the clutch gear. In the rotation gearbox there is a gear that allows slippage if the turret binds. Some guys don't like the slip, especially in battle. You would hear constant clicking of the clutch slipping if this was a problem, which isn't what you have going on. The clutch is there to protect you from damaging stuff if you twist the wires too much by going in one direction (if you go 6 full rotations left with never traversing right, your wires become a knot) or if you whack the main gun on an object, it allows the turret to slip free without snapping something. It's really not a bad design, nor something that has to be done unless you find it a problem. I didn't find it an issue until I was battling, but then a certain amount of abuse is expected.