Well, to be honest at 3:45 I'm just not motivated enuf to dig out the factory manual to look, but I WILL take a gander at it 8 or 10 hrs from now when I wake my a$$ up. However, I looked some of this over last week on an unrelated question and didn't see any notations about TPS adjustments effecting the 3-4 shift. You mention having an AOD. The AOD's are *really* touchy when it comes to the throttle pressure. If it's out of adjustment then it causes late/slow shifts and the sort of problems you're describing. In a 22yr old truck *I* would take it to a tranny shop to have the throttle pressure ck'd & properly set. It's also a good idea to have it ck'd because an out-of-whack throttle pressure is something like THE #1 reason AOD's burn up. Having it ck'd and adjusted every several yrs is NOT bad advise.
As far as Shift's comment goes, either the speedo *was* recal'd for the current tire size or it wasn't. There's no middle ground. Larger tires on an 86' will require a new speedo gear. You can either have a local speedo shop look at it and get you what you need or contact the tech-support line from one of the larger 4x4 retailers and they'll be able to tell you what gear you'll need for the tire you're running, but if you haven't replaced a speedo gear then you haven't corrected the speedo for the tires.
