1998 Ltd. transmission problems

'98 GCLtd. 5.2 V8 - just got the evaporator core replaced and oil changed. Now, the transmission shifts at lower rpm and doesn't feel right when cruising on the highway - when I let go of the gas, the rpm drops down to about 1500 and it feels like something is holding the car back and keeping it from coasting (overdrive clutch maybe?). The steering wheel has also always shuddered at (and only at 55 mph - ???).

I thought maybe my transmission would act funny if they topped off my transmission fluid with the incorrect type, or they disconnected my battery to replace the evaporator core and reset the electronics that store information about the way I drive.

Any thoughts?