I'm having this weird Engine problem. It started last night, I think. Driving down the road the truck barely runs at ~600-1000 RPMs, no matter the gear or speed. It will stumble on take off, and it will stumble after an upshift and the RPMs drop. Now its been studdering for a few seconds at first start-up in the morning for a while now, not sure if that was an indicator or not. Any thoughts or tips on how I should go about fixing this? Thanks!