Post Tune-Up Problems - ALL Advice Appreciated

I got a tune-up (spark plugs, wires, distributor cap and rotor, air filter, fuel filter, fuel injection system clean, and they also replaced the valve gasket? (which was supposedly recommended to ease the rough idling) *which i roll my eyes at that now.. cuz NOW it really does idle rough compared to what he said it did prior*
all this on my
99 Sebring LXi (V6) like 2 weeks ago (At Goodyear) ..and every since then its been acting weird in some circumstances and instances

I usually turn on my a/c on high during the hottest time of the day 12pm-4pm and thats when it all goes wacko... i turn on the car and it will idle rougher (like vibrates r shakes?) than it use to prior to the tune-up and when i reverse it feels like it looses power and shakes/jolts....and its like u have to give it gas for the lose of power to go away? and the Servive Engine Soon light starts blinking alot... but after a while it will go away (SOMETIMES) others it stays for a few hours then goes off. Also sometimes it will make a clank clank sound (or is its knocking sound?)... what do you suppose the problem is?

These episodes have started about 1-2 days after the tune-up when i went on a 3 hr trip to austin, tx..

i took the car to goodyear the following tuesday so they could check it out.. but OF COURSE when i took it early in the morning it wasnt acting up.. and the service engine light was off.... so they really couldnt see what was going wrong with it...has this ever happened to any of yall??

I don't know if its just the HOT weather that causes this? or the combination of the HOT weather and A/C being turned on at the same time... cuz when I turn my ac on in the early morning r night which is rare it wont really happened.... with the exception that it happened during the nights the first weekend -- could it be the fuel injectors? do u think they maybe messed up on the removal and replacement of plenum?

Im taking it back tommorrow.. around 1pm ( which is probably when it will start going wacky since ill turn on the a/c and it ill be hott and hopefully itll stay like that til i get to good year so they can see for themselves whats happening..
we will see what happens

In addition .. I used to have a 01 pontiac grand am -- that used to idle rough alot too.. and when my brother changed the module (r one of the modules under the fuel injectors r under the spark plugs) the shaking (rough idling stoppped) ---- do u think that module could add to the rough idling? --- the sebring is not idling as rought as the pontiac.. but its enough to bug the heck out of me

ask them to check the firing order, make sure they didn't cross any plug wires together, that would cause a rough idle. If they had to remove the upper intake plenum to get to the back 3 plugs, they probably forgot the replace the gasket, causing you vacuum leaks which can also cause rough idle. Last, have them check your engine grounds. A computer needs power and ground, basic electrical principles. If the ground is bad, you'll have a variety of problems, and with a 6 year old car like yours, you might have some bad ground wires that could be acting up as well.