Loss of power at start, slow to rev up and no guts on acceleration.

NO codes? Yup clogged fuel injectors could cause that. BTW did you or them change the spark plugs atfer you did this and did they clean out the throttle body as well? Normally a good injector servicing where they run solvent thru the fuel rail and into and out of the injectors runs about 150. After this the plugs are dead and need new ones. Did they do this or just pur stuff into the gas tank and spray the throttle body. Either of these will not need a plug change, only if solvent was directly used in the fuel rail. When I do this I do the 3 stage of throttle body, fuel rail and then change plugs to the iriduim champions.