Massey 2805 will not pull. Used the tractor about 5 months ago under heavy load, and got back in trans would not move. Looked at the fluid after I fired it up and it was 5 gallons low. Was thinking it was a slipping clutch, but I can go through all the gears and the 3 speed powershift and the audible humm it makes gets more pronounced as you go from 1st through 8. In other words, when you put it in first, you can hear gears working and they make a hummm, as you go through the gears on up to 8, the gears sound like they are moving faster. I suppose I need to get a service manual to perform some tests. Anyone had a similar experience?