Check the fluid level using instructions in the owner's manual (check
transmission hot after driving in all gears while idling in neutral with
parking brake set).  Slow engagement, especially when cold is a possible
sign of low fluid level.

If the fluid level is in the OK range and near the top mark, then I'd
suggest getting the fluid and filter  changed.  This requires dropping the
trans pan and is messy since there is no drain plug and they use RTV sealant
(no real gasket from the factory).  At your vehicle's mileage, I'd suggest
dropping the pan, cleaning out the gunk at the bottom using brake cleaner
and a clean rag or paper towels, removing and cleaning the pan magnet at the
bottom, and then replacing the filter, then reassembling using the
re-useable metal/silicone gasket (Chrysler dealer item) and then refilling
with fresh ATF+4 fluid (also dealer item).

If this does not fix the problem, it could be an electric solenoid sticking,
but since it usually works I doubt this is the problem.  Look at the fluid
first before you spend major $$$.

These transmissions can be finicky (use only the correct fluid and no
additives), but the reliability has vastly improved if they are properly
maintained.  I drop the pan and do this on all 4 of my Chrysler
transmissions every 30-36K miles.  One has 128K, and the others less, but no
major trans problems to date on any of them.

Good luck.

  Bob