I have a 2001 F150 with the 5.4 "L" code. I was receiving an occasional misfire code and lean bank code. Since they would come and go I ignored them (I know I shouldn't do that, I checked for vac leak a few times but came up empty). Well it started running rough, and REALLY rough between 1200-1700 rpm while driving (more of a ridiculous shaking, that made me immediately let off the gas). I noticed the smell of antifreeze, but didn't see any leaks. This weekend I had a better chance to look at it. Ran a compression checks had two cylinders that were lower, but all above 150 ( two low ones on opposite banks, not next to each other ). I thought it may be Bad head or head gasket, but the comp test was ok.
Then I noticed a puddle of coolant below the intake manifold, on top of the block. I was sure I had a bad intake mani gasket (lean bank codes, misfires codes, ridiculous rough running, coolant puddles under intake). But when I got down to the gasket there was no obvious problem. They were a little brittle, and one had a small tear (but this may have happened during removal because there was no obvious path for the coolant, it still had dirt built up outside the gasket.
I don't want to reassemble until I find a smoking gun, because taking it apart was a PITA knuckle buster.
PS- I have a coolant pipe under the intake that goes to the fire wall, not the hose that may have been on some earlier models.