i have a 2003 gmc envoy xl slt the abs & break light will come on at about 40 -45 mph following a slight shutter when i turn the truck off and back on the lights are gone the cycle starts all over took it to the dealer they re calibrated the computer system told me that it was my transmission and replaced my thermostat do i have 2 problems or 1 big problem

If the ABS light is comming on it is an ABS problem. Have them check again or try someone else.