Manual: driving my truck on 1st gear, as it goes there's a jerking motion like the gear is hitching back or feels like it's slipping then I shift to 2nd gear and it does the same thing...I shift up to 3rd and its becomes ok. but this happens every time. I couldnt get my truck to ride up the hill on 1st and 2nd gear...I had the hardest time...I rolled back down and started very slowly up hill til I got to the top. I get out of truck and there's a very heavy smell as if I burned something in engine. I'm told it's the rear differential and berrings rear axle area of truck... your advice would be much appreciated! Thank you!