Newly registered to the site, 1st time Ford owner, never thougt it would happen but i got a great deal on the truck from a friend, so i could pass it up.

I have 99 Ford F150 XLT supercab 4x4 w/ the 5.4l engine; however, when i bought it has a noise coming from approx. lower engine. The previous owner had a mechanic friend check it out and he believed that it is lower engine damage possibly/probably spun bearing (was quoted 1500-2k). The noise really only can be heard if the engine runs alil harder ie. downshifts/ running above 2500 and when it shifts back down below 2500. I am an experienced/non cert mechanic.. rebuilt/ built roughly 5 engines but only on Dodge and Chevy muscle cars...

?'s
1. the truck only has 87k miles on it, has anyone else had a problem with like this (supposedly the truck had regular oil changes and never abused *trusted friend of the family)
2. it still runs ok but looking to the future would it be best/ cost effective plan for the trucks engine
3A. Would i encounter any problems if i was to swap it with a newer 5.4 ie 3V
3B. Advantages/ Disadvantages ... more power and better gas mileage (currently i average around 12 mpg, the truck is basically stock but bigger tires that give it a little lifted look to it, will be adding exhaust, intake and tonneau cover soon)

Thanks...David

PS I've already utilized the forum for the diagram and info on replacing the Heater Core, the truck was down for a day but saved $$$$$. much appreciative for that