Al Smith
Mac Daddy
While I'm in my thinking mode another thought crossed my mind . You could have a brake band that either is out of adjustment or all oiled up from transmission or final drive oil leakage .If that old D7 is like the D4 the kerosene treatment might clear that up too . Trying to trouble shoot an old dozer over the internet is about like doing a chainsaw ,Best advice I can give is just a shot in the dark .I'll keep an eye on this thread