No Vacuum

Have an 88 w/ 3.1. Problem Runs rough at idle and at higher speeds ( if you can speed up ) Checked Engine vacuum - runs at 5" or less, can not hear any hissing. If it runs for a about 30 seconds the vacuum increases to 22 - 25 ", then drops off. Checked and capped off vacuum lines, blocked off EGR valve, Replaced PCV Valve and hose, replaced intake manifold and plenum gaskets, replaced o-rings on injectors.
I was told to check the timing chain for any slack, There is some slack in the chain. How much is too much slack????
Yes there are multiple questions.