When driving the car it gets to around 10-15mph then it wont go any faster. does that mean the transmission is going out or could it be a sensor?

i did a quick test drive but i bought it as is. Only paid $200 so wasnt too worried about the problem, i found some transmissions for a decent price so was just wondering if it was a sensor before i changed transmissions.

Then you should have it professionally scan tested, FULL scan test of ALL modules.. not a code read at some parts store!