Car stops coming up hill runs smooth for twenty miles and just stops

SOURCE: Car starts, drive a mile, stalls.

try haviing your alternator checked advance auto parts can check it while its on the car and the can check the battery too. if thats not it it may stall due to a loose battery connection or a loose ground strap. if it stalls and everything turns of (electrical) it may be a connection or ground strap.

SOURCE: at various times all the warning lights go on/off

i HAD THE SAME EXACT PROBLEM WITH MY CAR. IT HAS BEEN AT THE DEALER FOR 2 MONTHS UNTIL THEY FIGURED OUT WHAT HAPPENED. WHAT WAS WRONG WITH IT WAS THE MAIN CONNECTOR THAT CONNECT THE COMPUTER AND ALL THE MODULES. iT WAS FILLED UP WITH SODA THAT I HAVE SPILLED INSIDE A CAN COUPLE OFTIMES WHICH CAUSED A ELECTRICAL BREAKOUT AND ALL THOSE WARNINGS POPPING UP AS WELL AS LIGHT BULBS MULTIPLE FAILURE AND ALL SORT OF ELECTRICAL ISSUES.

SOURCE: 2001 Buick LeSabre auto transmission shifting hard sometimes

See if this helps try changing the transmission fluid and filter also add some Lucas Transmission fix.

SOURCE: Car cuts off!!!?????

This happened to me with my Ford Focus. Diagnostic with onboard computer said key problem, as in the chip in the key had sent incorrect alarm signal and that was why engine had cut.
Solution? New key from car dealership. Problem solved.

SOURCE: Chevrolet automatic transmission turbo 350

Was this a preexisting problem if not verify that the trani fluid type was correct. It should have been dexron or Dexron 2 fluid(not mercon products) check the fluid level over filling can be just as bad as underfilling)