I am having a similar problem....although I just purchased a 99 xlt (used)...(of course)...and I felt it when I test drove it. The truck is in near perfect condition so I wanted it. They said they would fix the issue that I had pointed out. Similar to what u r describing. A mechanic at a shop that will be doing the work has said that mine is a rear differential issue. So Ia m going to have them do that...getting a new rear diff is never a bad thing...than I am going to take it to a mechanic that I know personally have him take a look at the leaf springs cause he said that from what I was telling him it sounded like, he has had to fix rangers in the past that had the same issue. He thinks that is a flaw in the design that seems to be inherent in the ranger. Either way I get a new diff....no pain on my part....LOL....I will post results next week when I have the work done.
99 Ranger XLT 4.0l AT
Alpine HU / XM Radio
1 - 12'' Pioneer w/ Phoenix Gold 500 watt amp
To Do list:
To much to name here...lol