Having issues with my transmission. have a 84 m1008 that now has about 45k on it, got it 3 years ago with 22K. When out plowing for 2-3 hours reverse will only engage at high rpms (slipping). It only does it when the truck has been plowing for several hours straight, no other issues in any gear. Fluid level is good, its been 2 years since a filter change for the transmission. After the truck cools it is back to shifting fine, actually the truck shifts great unless it has been plowing. I think the reverse bands are getting weak when the fluid is hot not enough resistance but was thinking about plugging the "cooler" lines because I think the diesel is heating the trans fluid. If plugging the lines helps then I would add a external cooler. Any advice on this would be greatly appreciated.