New Exhaust....Now Overheating...WHAT?!

OK Guys here's the deal, spent Saturday (yesterday) installing UPR x-pipe and magnaflow catback on the 5.0 . Took it for a test drive and man, it woke up the stock (down to the paper filter and snorkel) car alot. Now I am running hot . It used to hover around the middle of the guage now it spikes at the bottom of the N on the temp guage, and hovers around the O. What's up? I replaced the heater core and basicly flushed the cooling system in the process. I don't know the age of the thermostat but I can see it working. I need your guys help I don't want to fry the stang right after I just bolted on some upgrades. Any suggestion would be great.

Already searched and couldn't find a thing. I have been running fine on the heater core for months now with no problems (made sure to burp the system pretty good) this was a night and day event. Day before drove the car hard and no temp change. Now peaking out high. Don't have a clue. Anyone else?

that's what I thought too. The revs come much quicker with a 2.5 from headers back rather than stock with weld in flows. I should look into replacing that stuff but hey that takes money.