Why is my truck blowing the dipstick out?

I would check the pcv valve it might be stuck

Jasper's are excellent guaranteed , like my buddy says the PCV valve is buggered up...pull it and inspect to see why? perhaps an oil change was never done~....the HOSE that connects may be plugged~ see the parts involved...be sure they are all there~ https://www.google.com/? gws_rd=ssl#q=1988+toyota+pickup+pcv+valve&tbm=shop

fluid level could be over-filled~ filter should be NEW~

Thanks Bob, but I already replaced the PVC and the hose as well as the dipstick. Do you if any of the vacuum switches on the valve cover controls the pressure inside the engine?

well rocketbob3...this is a puzzle for me too...one might ask, "where is the pressure originating? oil flow comes out of the pump and splits to the valves and mail bearings~ then drips out from the head onto the oil jacket, where the dipstick is extra pressure might be from a heavy-duty oil pump..(in your timing case) just look at this thread...would not recommend any drilling~ http://board.marlincrawler.com/index.php?topic=92815.0