06 Engine Issues.. What to build..

Ok.. I had an '06 Rubi with all the normal cam/lifter issues.. #4 wiped out completely.. 2nd time for #4 cyl.. 3rd major repair.. first being the oil pump drive gear that eliminated all oil pressure.. Either way.... Jeep denied the warranty.. I found an engine on craigslist from an 04 Grand Cherokee. pulled it apart with 54k on the clock, and rebuilt it.. new cam, crank, lifters, bearings, gaskets, water pump, thermostat, reconditioned head,.. stock manifolds, sensors and the like.. installed in my jeep with a mechanical oil pressure gauge and now I've got a brand new motor that gives me low oil pressure.. btw.. it's got a high volume melling oil pump and pickup.. (brand new) .. This engine now has 250 miles and I'm getting low oil pressure not only at idle.. but.. at 2500 rpms I'm at like 15-17 psi.. at 3000 rpms I'm just touching 20psi.. but.. when I stop it will drop to below 10, and then finally to zero.. but.. it does seem to run like a top. I didn't buy a cheap gauge. I got a $65 2" mechanical Auto Meter Pro Lite Gauge.. Should I be worried?

On top of this.. I'm going to file a complaint with Jeep / Chrysler.. Does anyone have a suggestion for how to get ahold of their complaint department.. Whether my jeep was out of warranty or not, the parts should last longer than 8400 miles.. even if it was 12 months and 5 days vs 12 months.. (they're actually denying a claim that's out of warranty for 5 days.. after it's doing this for the 3rd time now.. ) Was wondering if anyone has had any luck.. My local dealership is garbage.. I wouldn't let them install a headlight.. (btw.. they broke my headlight bucket last time they tried to adjust them for me.. nice guys.. and then didn't tell me about it.. ) But.. I do have a dealership about 30 miles away that will help the best they can.. Any numbers to call or addresses to right..

And.. as far as the what to build question.. I see a bunch of people suggesting that you build a 00-02 4.0 engine.. I see everyone suggesting it but I can't seem to find a difference.. all the parts #'s are the same according to chrysler.. same cam, same bearings.. what's so different?? head castings? crank??? I'm lost.. I'd really like to build a reliable motor that I can toss in this thing and be done working on it for 10 years.. any suggestions? and if you suggest a 00-02.. why?