Hi I have a 94 Deville and it cuts off sometimes, I put it in the shop got a new map sensor. Now its having problems shifting, change gears, going in reverse, the car will not show any codes had it ran twice came up with nothing. If its park on a incline it will cut off ,and come back on but then it what shift for awhile. Please if anyone could help before I spend alot of money ,I would just like to know what the problem could be.

 

Grounds are always possible, condition of battery cables and connections, last suggestion if wiring harness going across rear valve cover is it metal clamp type retainers - release it from retainers - check wires for chaffing. Metal clamps can cut in to harness causing multiple intermitted problems. Do not re-intall harness into clamps.