Engine miss with A/C on
 

1993 S10 2.8 v6 5 spd. A?C I bought this truck 6 months ago and have been working through misc small issues. I've replaced plugs & wires, rotor & cap, ignition coil, egr valve and iac valve, and fuel filter. When A/C is on the engine misses at speed but not at idle, when A/C is off, engine pulls strong, no missing, no fuel starvation. Could this be a bad battery, alternator, or bad connection or ground? Had vacuum leaks and I think I got all of those. How to test when only happens when at speed?

I'd think this is a low horsepower issue, do a compression test