Hi I bought a 2000 Chevy C3500 with a 6.5L turbo diesel a few weeks ago. Last week on the way to work a Whining noise started and all of a sudden I noticed the truck couldn't get out of it's own way. The issue is intermittent because when I drove home it didn't do it. And today when I went to advance auto to get a part it did it again but on the way home it was perfectly fine. I have 3 things that I feel it possibly could be. My first though is the vacuum pump went bad causing the waste gate to not be held closed. My air vent switch seems to have stopped working and air comes equally out of every port. Not sure if that's related because it's possible I broke it when I ripped apart the dashboard and put it back together. And the switch doesn't feel right. it feels like a mixer switch instead of a selector switch. Not sure if it should feel that way because I'm used to ford selector switches that index at each vent mode and if the fords I'm used to has a vacuum problem the vents become stuck on defrost and air doesn't equally come out of every vent. 2nd possibility is maybe fuel pump. (in theory the pump could make a noise and truck have no power due to lean fuel) But engine seems to start fine and usually starts before it makes a full revaluation. I would expect to it crack for a long time if it was having a hard time getting fuel. 3rd is probably worst case and really hoping it's not the issue. But maybe transmission related? When I first bought the truck the trans was 3.5 quarts low on fluid and now that I got it topped up it smells burnt. Planning on servicing the trans and hoping it will last me at lease a year before needing a rebuild. But manually shifted through the gears still feels like I have every gear it just feels like there's no power to get where I'm trying to go and doesn't really want to go above 45mph when the whining is happening. The first time it happened I noticed if I stomp on the gas white smoke would come out of the tailpipe. But today when it happened again I stomped on the gas and the pipe remained clear. What can I check to confirm what needs replacing. After the past year I don't have money to just shotgun parts at this truck. I only have money to fix what needs fixing. Thanks!