Hello I have a 1992 GMC C2500 with a 5.7 Auto. The first problem I had was the RPM would jump a few 100 while driving with no increase in power or the lurch forward I would expect from the RPM increase. also under moderate to hard acceleration the jump would go away. Then some more issues came up as well as a CEL when I pulled out the trusty fork to pull the OBDI codes I learned it was a coolant sensor and O2 sensor. After replacement the truck drove great. Still the RPM was jumping, and soon wanted to stall at a stop light or going into reverse. Yesterday while driving it tried to stall at a stop light so I put it into neutral to avoid it dying. When I then put it back into drive there was a horrible grinding noise, so I pulled off the road and poped the hood and everything looked fine, made it to a gas station and checked the trans fluid and it was low so I added a quart and the noise lessened. On the drive home I noticed the trans shifted fine and I tried all the gears and all the gears worked and the noise was still there. Once up to speed say above 45mph the noise goes away completely and the truck drives like I am used to with the RPM jump as usual. Once you come to a stop the noise gets louder and the rpm jumps up and a you get aloud winding up noise with the grinding then it stops and goes to just a slight grinding. also during idle you get a slight grinding. Please help.