trooper timing belt replacement 1999

im doing a timing belt on a 3.5 trooper and each time i put the belt on the cams are correct but i keep coming up one tooth off with the crank, what is the trick? when i go to put the belt in place i get all the slack i can by rotating the cams in opposite directions so they are alligned and the belt is tight between them but i still dont have enough to get the mark on the belt to the correct tooth on the crank. so it causes me to bring the crank gear just a touch back towards the alignment spot to catch the correct spot on the gear. i then release the tensioner and do a full rotation. when i get back to tdc. all is correct except the crank gear is off by a full tooth. i hate these damn things and i had allmost the same exact problem with a 3.2 in a rodeo if this was not one of my best customers and the girl hot as hell i would have never taken this nightmare, it is not only a belt it's a whole motor swap. and she blew it up so bad the crank was hanging out the side of the block so i had to take the motor with the convertor, not to mention cut the pick up tube and oil pan off to get it to clear the front axcel!!