[Madda]

Your radio settings might be equal but I woud still try to adjust them and see if that makes things better or worse. This method can help answering the motors different speed question.
Then make sure that all the wires are correctly connected and not damaged from somewhere.
When my other radio started to die the motors began to glitch too and if you say that your rx is acting strangely then I would assume that there would be another problem. Maybe try to change the channels you are using for your motors atm to something else. If you use 1 and 2 channel for forward/back and steering then change them to 3 and 4 channel and see if anything changes etc. Someone with same radio can help you finding the problem.
I think that problem is somewhere in electronics but you never know.

Btw, what radio do you have?