Vibration - 2000 XLT

I own a 2000 Ford Ranger XLT, 4X2 supercab, with the 3.0 liter v-6....I have put 123000 miles on her, and luckily most of them have been highway. I have been noticing a fairly pronounced vibration while driving, it is noticable until 75, then is goes away. If I get off of the gas and then reaccelerate, I can really feel the vibration kicking in when the truck regains speed. I only seem to really notice this on the interstate, but it has me worried something major could be starting to go. I have always taken care of the truck with engine maint., but have not done any chassis replacements, shocks, struts, etc....If you have any thoughts as to what this might be...PLEASE HELP!!!
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Look at your U-jionts? Do you hear a "clunking" sound when you put it in gear? It sounds like it might be coming from you driveshaft.

Not really any sound when putting it in gear...It just does it when the engine is under power....Around 70 or so mph.

could be alot of things. shocks, tire balancing,tie rods,wheel bearings,ect. these are all things that will go at this millage.

If it's a manual shift 5 speed you need to check the gear lube in the tranny lickity split! I had a very similar situation and one day at about 80mph a metal on metal grinding noise exploded under me and the tranny was toasted!

There was no gear lube in the tranny!

There are several places gear lube can escape. One of them can happen so slowly you'll never know until it begins to growl at certain speeds. In the cab where the shifter meets up to the tranny, under the boot, there are 3 small bolts that go through a round plate holding the shifter in place. that round plate has a black rubber seal that if torn will allow gear lube to be slung out ever so slowly.

Mine started vibrating (a very low growl) at high speeds just as you describe. After the tranny failed I looked for the leak and couldn't find it. I replaced the tranny with one from a wreck and figured the old tranny had a leak I couldn't find. About 6 months later the growl was back. Sure enough the gear lube was gone again. This time - before it failed - I did some further searching and found the problem was the seal on the shifter which I had used from the old tranny. It leaks so slow that the lube works it's way from the shifter down the tranny toward the rear and never shows up as a puddle on the drive way. Drain the gear lube and see if it's low or worse, dry. If not, Check your U joints and your rear end's gear lube.

Thank you all for the responses, I did some checkin and in the end, had the front end re-aligned, wheels balanced, and shocks/springs replaced. 3 hours and 250 bucks later, I took her out onto Interstate 95 and got her going, and amazingly the vibration was/is gone. Drives as smooth as the day I bought it. I have a question about the transmission now, so see the new post...Thanks again.