i have a riddle for you. My daycare lady, mid 2000s chevy 1500, v8. Randomly stumbles, especially in drive thrus. She's paid 3k so far in parts and labor and they still can't figure it out. Has new injectors, new rail, new fuel pump, new throttle body, new TPS, new filters, new plugs, plug wires, coil packs. Its not tripping any codes. Gets worse when its is raining. I'm thinking may a ground issue?