focusyn

what is CEL code?
is the new tranny shifting into OD and can u tell if it's going into torque converter lockup which is not as noticible? either not working, major effect on gas mileage.

depending on what was replaced in auto tranny, full master rebuild-all clutch packs, torque converter, bushings, bearings etc, turning resistance will be higher until broke in.
if just a quicky band-clutch disk replace, then you have other problems than auto.
take back to tranny shop and get the problem on record.