I have a 2002 dodge ram with 150k miles. I had it in the shop for two weeks getting body work done. All the sudden I drove off and my check gauges light came on. And it's only the oil pressure gauge. It was fine I drove it home. This morning on the way to work. Felt like it kept staying in high gear and wouldn't switch. I wasn't sure cause I was in a hurry to notice. I park my truck at work and all the sudden my engine sounds like its crackling. What could this be???

 

Might check the oil first.
Where on the truck was the bodywork done?