RPM's increase from Park to Drive...

I just got my freshly rebuilt 327/th350 running in my camaro this weekend and wanted to take it for a test drive but the rpm's shot up to 1500 when shifted into drive. It idles in Park at 800. When put in reverse, the rpm's drop down like normal.....any help would be greatly appreciated. :confused:

never heard of this block your vacumn line to the trans and see what happens??? what year camaro

Throttle cable rigged wrong and something pulling the cable when you move the shifter to drive????