Rusty, buy/borrow an ammeter that loops around one of the hot leads and determine at what psi the motor reaches full load amps. This should be stamped on the data plate on motor.It could be a problem developing in the motor.
Mike

Thanks, Mike! I'll get an electrician buddy to check it out!
Rusty

The 70LB window is usually incured with a bad check valve.
Check that first. If it is ok then the valves and or rings woul be the next suspect.

Rusty, what did you find on the air comp.
Mike

Sanding dust, oil mist, a few mouse turds, but, all kidding aside, i haven't had time to check it!
Yesterday, i turned it on, it ran all the way up to full shut-off pressure, and shut itself off like it should! Sometimes, if the sun shines on the shut-off switch, it will do that, but yesterday the sun wasn't on it! If i shine a heat lamp on it, sometimes that helps, but not always!
I guess i'd better get a main shut-off thing, and a check valve, and go at it.
Although, last year, i took off the check valve, soaked it in laquer thinner, blew it out, and it worked for a while. I'm going to try that again-it may be the problem!
Thanks: rustyj

Your check valve is sticking, but not stuck open.
Disassemble and clean and oil..
My el-cheapo compressor leaks like a stuck pig.
I replaced an O ring at the check valve and re-tightened everything, also replaced the ribbon dope with Permantex thread sealer.
Used the brush and soapy water - bubbles everywhere !
You have a good compressor,IMO..