Spends over an extra 5 seconds before cranking?

I have a 2000 chevy suburban when I try to crank it in the morning or on a regular drive it spends over an extra 5 seconds before cranking. Sometimes after driving for a while and stop at a light it has a rough idle. I have put it on the diagnostic machine, checked o.K, I have sent it to a mechanic he cleaned the trottle body still contiue to do the same thing. I dont know what else to do I hoping its not the timing going bad.