Please help 5.7 vortec

If you haven't done so already I'd suggest replacing the spark plug wires. Since the spark plugs, distributor cap and distributor rotor are new and the ignition timing is correct bad plug wires will cause a misfire, especially in wet weather and under higher speed driving. Also, given the age of your truck, I'd do a compression test. If one cylinder tests considerably lower than the rest you have a weak cylinder. That could be a piston ring problem or a valve problem on that cylinder. If that's the case it's time for an engine rebuild or replacement. Hope that helps! Jim

Thank you. just had the plugs and wires also changed. I'll start with a compression test this weekend if the weather let's me outside. I didn't think u could set the timeing by hand on my motor? Midas said they messed with it when I had them scan it.. Could that be why she's running like crap now? Has me on fire since I only asked them to scan it. Drove fine besides a slight miss at 50. When I had the tranny put in its the right one but they said no and that it burnt up my computer.. Again wasn't having transmission issues when I took my truck to them.

You're welcome. Glad to help. The ignition timing is set by moving the distributor while shining a timing light on the harmonic balancer. There's timing marks on the harmonic balancer and as you move the distributor the timing marks will move. When you have the timing mark lined up properly the ignition is properly set. Your engine may only have one timing mark on the harmonic balancer and one mark on the engine instead of the older style "sawtooth" timing marks on the engine but the idea is the same. When viewed with a timing light the two marks should be lined up for correct ignition timing. Unfortunately the 18 year old "tech" at Midas probably has no idea how to check or adjust the ignition timing with a distributor type of ignition system. I ran into a similar problem with the security system on my 94 Fleetwood. Long story short I was told the ignition lock cylinder was the problem after a $700 diagnostics charge. I took the car home, studied how the system works, and fixed it myself. It was the body control module that cost me $200. I should have fixed it myself in the first place! Hope that helps! Jim