i have a 88 k5 blazer all stock including tires (due to lack of time and funds at this time). i have a very hard knock in my drivetrane at an idle(after warming up) and my oilpressure holds about 15 psi. when i start down the road the knocking goes away and the oil pressure does fine. until i get to about 55 every thing work great except for second gear has some sliping and some times third will slip. but it does not slip at all when driving like grandpa. when you get to 55 the is a hard vibration that travils throgh the drive train like ann unbalanced drive shaft. i have changed the tourge converter te oil pump and trans filter. ido not believe that the rear main is knocking i believe it is the trany. also after puting my foot in if the windows are down you can smell the trans baking from heat, but i have a cooler and it is bypassed the radiator. anybody ever heard of something like this or is this just another one of these things that just happen to me and no one else. any input would be greatly apreciated.