I asked if it had a plow because I had a simular problem with my 84F250. It pulled no matter what I did.A friend told me to check the left front tube beam he had seen this aseveral times. It was cracked near the Ubolts where the springs and the spring plates are (real close to them).I put in a new tube (out of a bronco Mel) and it was fine after that. I have seen that since then on Plow vehicles. So I would check that out too.I'm not saying that is the only cause ,but one that should not be overlooked.