vibration

i really need some thoughts on my 86 bronco 302 efi aod. i can take off fast and no vibration up to 2500 rpm. after the tranny does its shifting(in OD) the vibration starts about 1600 rpm. If i run it at 1600 rpm and shift into N there is no vibration. i tap the gas while at speed in N , and there is no vibration at any rpm.what do you guys think? thanks, Gary P.S. I just repaced all 4 tires

If you take it out of over drive and manually run it in other gears over 1600 rpm does it still vibrate or is it only in 4th/ O-D? if only in o-d at higer speeds:
Were the tires balanced? Maybe one of the wheel weights flew of and causes the wheel to Vibrate at higher speeds. is there mud caked on one side of the rim? there are a number of things it can be. It could be a U-Joint going bad. Or it could be the overdrive gear in the tranny starting to go. If in other gears it may be the torque converter. Is their 4-wheel drive on it and if so do you have manual or electric hubs. I am not that good with automatics so you might want to call a reputable trans shop for info on poss. trans/converter problems. Hope this helps or atleast gives you some things to check.