My neighbor and I each have a Ford F250 PowerStroke with automatic transmission, and we had a strange thing happen with his the other day. He had a 3500 lb trailer loaded with bark attached and I was backing it up his driveway. The driveway is pretty long (300-500 feet), curvey with a dog-leg, and up-grade, and the trailer has electric brakes that weren’t connected. It all seemed OK at first, but then it gradually started to resist the attempts to continue backing. The further I backed, the more throttle I had to apply. I had to shift once to go forward to handle the dog-leg and there was no resistance going forward (actually, I just costed forward). After getting lined up after the dog-leg, the resistance to backward motion continued to increase. After getting the trailer positioned where he wanted it, we noticed that the transmission had been spraying ATF during the last part of the backing.
The next morning he drove the truck without any signs of trouble, no unusual resistance and no spraying of ATF.
1). What might have been happening that caused the increased resistance and the spraying?
2). What corrective action could I have taken when I noticed the increased resistance?
3). Might his tranny have suffered damage?
4). Is this something that could happen on my truck (it has SB 99-3-5 installed).