Howdy
OK....couple of issues, I will start with the minor one-
1986 blazer with 6.2 T400 trans. Speedo was off by about 10-15 MPH, lubed the cable got a little better but not much. kinda bouncing around. When I replaced my tires I went with larger ones. Now when the truck is cold the speedo reads almost right on, things warm up and I get the bounce and it might be right on or off by about 5MPH. I thought these speedos were a direct gear/cable drive. So...it should work or NOT work, right

Next question-
!996 3500 dually 4l80e trans. NO REVERSE Happened very suddenly with no other trans problem symptoms. No noises or slippage, went to put it in reverse and no go.
It works perfect with nice hard shifts in all gears. Fluid is red with no stink or metal. No noise from trans mission. No indications of shift issues or drivability except for the no reverse. Any help????

Thanks!