So many possibilities...

does it roll fairly freely? (checking to see if the brakes or rearend seized up)

Are there any "bad" sounds like things grinding? (Connection between Motor and rearend, axle splines...)

If all that is solid, it is likely in the controller.... (it takes a solid charge right... No bad batteries in there or loose connection? might want to check all the battery connections to make sure none are burnt...)

1997.. does it have the electonic speed control by that year? the other possibilty is that the accelerator is not working corectly. they used a resistor system on old ones that has contactors that would get worn out.... Newer ones control a potentiometer(sp) that controlled the speed.

Only a few real components to check, but if you are not mechanically and electically inclined, could be tough to isolate.

peace,