OneCoolPR

I have a 98 Tacoma 2.7L 4x4 automatic transmission. When I come to a stop; I feel like a thump at the rear or perhaps the transmission. The transmission oil was kinda dark so I had a Transmission flush with Toyota transmission oil brand. It helped a little. Now 5 months later I had Jiffy lube do the flush with their brand and if feels like it got worse. My mechanic tells me that it could be the rear brakes grabbing due to rear gear oil leak. I don't think that's the problem because when I shift into neutral before stopping; I don't hear the thump. Only on medium to hard stops. Any idea what this could be would help.. thanks in advance ..