Yes, you can use the regular GTB with Spektrum radios. The Spread Spectrum optimized version switches the FETs at a higher frequency that would interfere with standard radios, so you shouldn't go the other way (use a SS GTB with regular radios). Check the switch harness connector and wires. I had intermittent operation that turned out to be a broken wire in the the harness.
*** The Gate - Celebrating 7 years at the same location ***
The difference between genius and stupidity is that genius has its limits. - Albert Einstein
Understeer is when you hit the wall with the front of the car and oversteer is when you hit the wall with the rear of the car