Nope, a Toyota, but I don't get along with the Toy guys, so I'm here.
Same idea though, right?
You must be just like me (not getting along with the toyota people). It sounds like you have what is called bump steer. It is common for 79-85 toyota 4wd pickups with the "push pull" type steering to do this when a lift kit is added or larger or wider tires are added. The reason for this was that when they designed the steering system, they didnt design it to have huge tires and a lift (the steering system is by no means weak). The stock tires on one of those usually were either 235/75r15, or 31x10.5, and those tires cant put much force against your steering effort, but if you put larger tires on it, they can put a lot of force on the steering system, causing the steering wheel to spin with force. I have heard of a kit called a hi-steer kit, that converts the steering from the push pull to the style that the IFS trucks use, but you have to get an IFS steering box, and do some fabrication.
BTW today I came across a 1991 toyota 4wd 5spd extended cab at the honda dealer where I work, It was originally going to be traded in for $900 (keep in mind that this is a great deal for one with 54,000 miles on it), and I talked to my dad about it, and he said he would loan me the money. Well... I go to my work today, and it so happens that the guy did his homework, and then wanted to trade it in for $5000. When it was all said and done, he traded it in for $3000 and after the safety inspection, it would be $5000, and out of my reach :'( and to make matters worse, the car dealers owners son, who is the sales manager, is buying it to turn it into a rock crawler :'( :'(. It has to of been the nicest 1991 toyota pickup I have ever seen(at least 15 years from new) Its really too bad.