Transmision Slipping (09 JK)

I have a 09 JK.



I had a transmission fluid line to the first cooler changed the other day at the Chrysler dealership (Line was leaking).



Since then, after the JK has sat for a few hours, when I begin to drive, stop, then start again, the transmission slips, the engine revs, then it slams into 1st gear.



I then noticed when I put it in reverse, I had no reverse.



I cycled the gears a few times, then it went into reverse.



I just tried it again after it sat over night, same thing, started to drive, I stopped, then started again, it slipped, slamming into 1st gear after I revved the engine.



I drove a couple hundred feet, stopped, put it in reverse, again, no reverse until I revved the engine a couple times, which it then slammed into gear.



After it warms up, it runs fine, no slippage. So far, I have only noticed it when it is cold.



(Yes, transmission fluid level s good)



I am thinking there is air in the system.



Also, when transmission fluid is added, at the same time, aren't you supposed to cycle the gears as you fill it? The dealership said they did not do that.



Thanks as always for your expertise / help.



John