What you [personally] can and can't do without you [or a garage] playing 'parts darts' with your money. If the PRND etc box's are lit [cluster self check sequence] it means the TCM does not know which gear is selected. The 2nd, Neutral, Park & reverse are human and selected via mechanical linkage. 1st, 3rd & 4th are electronic and selected by the computer [TCM for petrol & EAXT for diesels] via an instruction to the solenoid pack. Most people can manage a fluid change, never flush just a drain & replace fluid. If you do a replace fluid many many people get lucky and it re-trains itself over a coule of hundred miles on the 41TE. If you like 'jasonleah1' are unlucky stop spending a penny till you get professional gearbox diagnosis or you will waste your money. Yes the module under the NSF wing & plastic cover has wiring that goes through a hole in the metal inner wing that is well known to chafe & expose shorting out wires. Best of luck.