Merry Christmas Everyone!

After stopping, my astro hestiates and backfires when we start rolling again. It doesn't make any sense because a mechanic just tuned it up (plugs, wires, dist. cap). During the tune-up he discovered the plugs were fouled due to bad injectors so I replaced them myself. It WAS running like a brand new vehicle until now - three or so days later. However, we haven't driven it much since all of the work was done. Any help would be greatly appreciated.

I have two questions for you. Question number 1: Did this backfire and hesitation problem start after the tune up, or was it doing it before also? Question number 2: Is the backfire coming from the intake, (under the hood area), or from the exhaust, (out of the tailpipe)?