Thunderbolt IV problems, will not run above idle when hot!

[Big Boat Bay Buster]

I have a Thunderbolt IV ignition, 1987 V8 5.7L. After cruising for 20 minuets or so, it bogs down. Idles fine, but wont go above 1200 RPM. After I shut the engine down and let it cool, it runs fine. I'm convinced its in the ignition system, notably the TB module (box on the exhaust manifold), but I want to be sure. At the start of the season I replaced the cap and rotor, replaced the original pick-up-no problems with the old system, just wanted to replace after 10 seasons. After problems started I checked all my work, spark plug/wires changed fuel/water separator. Changed the coil also
Other things to note--Tachometer drops to almost zero when engines starts to stumble when increasing throttle. Also, voltage gauge drops when RPM's increase as if there is a large draw-replaced alternator and still have a voltage drop.
Fuel system is in good shape.
I would like to go with a one wire, new distributor/ignition system upgrade--any recommendations??
Any ideas on what might be wrong?
Thanks, Chris​

 

[alldodge]

After cruising for 20 minuets or so, it bogs down

When it does this have you opened the gas cap and listen for air rushing in?

 

[achris]

Throw a timing light on a spark plug lead and CONFIRM you are losing spark.

Chris.......

 

[Big Boat Bay Buster]

Problem solved---Long story short, I put back the old magnetic pick-up in the distributor since I know it worked good. All issues disappeared!