Change the fuel filters first. My SD did exactly that. There may be a reason that they are plugged ie fouled tank pick up. But begin there. Of course, it could be tranny but also highly likely it is fuel related. Start with the cheap stuff first.

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85SD 240K & stopped counting painted, putting bac together. 84SD 180,000. sold to a neighbor and member here but I forget his handle. The 84 is much improved from when I had it. 85TD beginning to repair to DD status. Lots of stuff to do.