GMC Repair: gmc savanna 2500 misfires, gmc savanna, competent mechanic

Question
gmc savanna 2500 misfires when going up hills on highway. took it to 3 places did complete tune up, changed coil. check engine light still comes on?

Answer
Hi
First what year is van? What engine?
What could you get the codes (check engine light) codes for me and follow post back?
Have the injectors FLUSHED. If no help one or more MAY need replacing.
A mechanical problem can produce a misfire (worn camshaft lobe, weak compression [rings, valve bent etc...])
All these items SHOULD be checked be a competent mechanic or repair shop. If they (repair shops you used/are using) let the vehicle go and it is still misfiring.... you paid GOOD money for tune-ups so NOW DEMAND to have them fix the van now.....
Good Luck
Pawl