Idle surging at a stop
 

I just had my spark plugs, fuel filter and intake gaskets replaced last weekend. I immediately noticed that every 3rd or 4th stop at a stop sign/light it would drop rpm's from 500 down to 300 up to 500 etc for a few seconds before stalling. When moving it runs fine. Monday, Tuesday and Wednesday morning it only tried to stall twice each day. Wednesday afternoon on the way home from work it would surge from 500 rpm to 1000 down to 400 and back and forth the entire time I was stopped. In less than 5 miles it stalled 3 different times at 3 different red lights. Once I got home from the remainder of my 40 minute drive (highway, 4 stop signs and 1 red light) when I pulled in my driveway it idled fine (500rpm) in gear and in park. Any ideas of what the problem could be?
service engine light came on within 10 miles of leaving the shop that did the work last weekend. Already made an appointment for them to look at it this weekend.
2002 Silverado 1500 4.8l v8 221,000 miles
02 sensors, and MAF sensor replaced 2 months ago, battery and alternator replaced within the last year.

Won’t know for sure without codes but I’d guess the intake isn’t sealed properly. It could be one of the gaskets is misaligned, the manifold wasn’t properly torqued, or vacuum lines were damaged and leaking. It could also be the clamps on the intake boot weren’t tightened or the boot wasn’t properly seated on the throttle body (common problem).