Miss at high rpm Range when driving

hey i was wondering if anyone could tell me why my 89 E-250 misses when you are drving. when you floor it to pass someone it misses really bad i put a new distributor in it and complete tune up and a new coil and new fuel pumps i was wondering what ealse it could be. by the way it was a 300 straight 6. thanks if anyone knows please email me at alan_woods2002@yahoo.com. thanks a million

Double check the spark plugs. If they get a hairline crack (installed tight, dropped at parts place), it usually wont miss till you push the van hard. While you're at it, you may want to do a compression check.