Removed IHS to replace thermal paste on i5 3750k temps have INCREASED.

The stock intel coolers are kind of a pain in the ass. I've had several cases where I've thought the heatsink was in all the way, when in fact some of the pins aren't all the way snapped in. Double check that. Also, you made sure to clean off both the processor and the cooler with rubbing alcohol before you put new paste on didn't you? Did you spread a nice, thin even layer?

That is one of the parts I would not bother to take apart.

Arctic Silver is suppose to have a curing time (I believe 200 hrs?) during which time it's thermal properties improve but there is also a warning which I believe may apply for that application "(While much safer than electrically conductive silver and copper greases, Arctic Silver 5 should be kept away from electrical traces, pins, and leads. While it is not electrically conductive, the compound is very slightly capacitive and could potentially cause problems if it bridges two close-proximity electrical paths.)"
found here http://www.arcticsilver.com/as5.htm - I'm thinking the CPU itself may involve "close-proximity electrical paths".
I do not know for sure though

Read again brother, he took off the heat spreader, not the heat sink - the cap that protects the silicon die of the CPU.
As for you you filthy little tinkerer, i HOPE you didn't put too much paste in there - all you have to do was put enough to cover the die & connect to the spreader. Did you get the spreader back on nice & tight?

Chilled, you were correct. The heat sink wasn't snapped in correctly. i was barking up the wrong tree. Good advice. Thanks.