It will crank all day without a PCM, just not gonna start
Next, you should ALWAYS post your yr/mdl when asking for help...
Without a WTS and your swap it does sound like it's a power issue. Thing is, they're All fused so, and I don't mean to insult you here
, but in 99% of these cases it IS a fuse!
You have to Triple Check
, use a meter (or light) on Both sides, pull them out, wiggle them around, REALLY give everything a close examination.
Fuses #19-30-22 are among the most likely, I'm sure there are others that supply power also so, check 'em ALL.
Another thing can be the fusebox itself, a previous owner might have jammed one of those fuse-tappers along side a fuse and bent the "clip" inside so it now doesn't grab the fuse well.
Also, do you have a chip or tuner installed? a problem there can prevent the PCM from running, take it off as a Test.
Do you have any other things that aren't powered like they're supposed to?