opinions wanted about misfiring.

[pointer80]

Hello all. I have a 97 ext. cab 4x4 z71 that I just picked up. It has a constant misfire on number 4 cylinder. Also a occasional miss on number 6 cylinder. I have changed plugs and checked wires. I have put in cap and rotor. Did compression check and it came out great. What is the next step. My mechanic says maybe timing (which he is thinking of computer being bad throwing the timing off or maybe a injector? What do you guys think? Thank you in advance.