Engine Performance problem
2002 Jeep Grand Cherokee 6 cyl Four Wheel Drive Automatic 56400 miles

Problem started after having been into the shop where they replaced spark plugs, and flushed transmission.
When I am at a stop/ standstill ...(usually my first trip out driving the Jeep and driven a few miles) I press on the gas pedal to start driving again and it doesn't accelerate...it hesitates... and the acceleration from 20-30mph is very slow. Doesn't always happen but more than not on the first trip out . Once I am past 30mph it acts normal, no hesitation. I notice the tackometer stays at 100 when it is hesitating and at or near 210 when it is accelerating normal Please answer, this is happening more and more! thanks