Welcome to the forum,
Well, you can't get better advice than from BLUEH20 (us Navy guys gotta stick together) but one bad thing I read in your post is that you use Jiffy Lube.
The Lord only knows what kind of oil they threw in your PT or what kind of oil filter. I saw a report once on fast oil change places where they used an old (used) oil filter on someone else's brand new car.
I'd go to a reputable place (ask friends and neighbors for advise) and have the oil and filter changed again just to rule out anything that JL did.
In case it turns out to be the sending unit. Here's where it is.
