<100K miles. One morning I noticed it shifting very hard from 1st to 2nd & then losing road speed as engine speed increased. Assumed it was slipping. Returned home & checked fluid, none on stick. Truck is used <2000 miles/year & maintained reasonably well.. No ATF fluid on ground or underneath of truck, no ATF in radiator. Stick & fluid do not smell burnt, of course the fluid is new. Refilled transmission 3-4 quarts. Now truck accelerates away normally, upshifts to 2nd late & harsh. Climbing fairly steep hill I thought the trans was slipping but it appears to be downshifting back into 1st. Cycle through reverse, same thing. Holding brakes & accelerating the engine, seems fine, no slippage.