So after changing ignition coils (used) and coolant temp. sensor (used), with no change in problems, I did my own digging up in the car for a few days.
Wife started to doubt meh, telling meh I only making it worse and I'm not a mechanic.
Figured out, by a bit of luck, that the issue had to do with my EGR system. When I cleaned this part, it worked fine for a short while... but problems resurfaced. I then found a pic similar to the below on the Internet, but basically has the same information. Switched around the two hoses and car is now perfect!
Very relieved! Haven't told the two mechanics who had hands in changing the head and block yet though. I want to tell them just for their knowledge too. Everyone makes mistakes, but I just wish I didn't spend all the money trying to figure it out.