take the back valve cover off and check that every thing is moving right, you will need to start it up for a minute. both middle rockers and push rods and the springs.

if the springs look ok and the rockers are ok, try to spin the push rods, they should be straight so watch them as you spin them.

also make sure the rocker bolts didnt back off. did you get new rocker nuts? or reused the old ones? you supposed to use new, the factory ones are one time use. tty