Classic/Antique Car Repair: 396 re-build, good luck jack, chevy car

Question
total re-build of 396 cu.in 325 h.p. shop installed a Comp Cam Part#11-242-3, grind #XE26BH-10, resulting in rough idle and low vacumm, not happy with the results, can you advise mod. to correct.  This is installed in 1969 El Camino.  tks Al

Answer
I'm sorry, but I really don't know anything about go-fast equipment.  Try to find a chevy car club and ask them.  If you can find one near you, join it and you can have a lot more fun with your car and get a lot of help too.  Performance cams usually cause very rough idle, but I don't understand the low vacuum.  Some valves are staying open too long.
I know Model A's, not cars like this.
Good luck.
jack