ok,solved. After all the parts swapping, computer scans ect.. turns out the kill switch had a bad contact inside. I thought I had bypassed it a few days a go.I unplugged it and checked for proper operation then plugged back in. I went out this am with a fresh set of eyes and with the key on, engine off, my buddy noticed the trim tab lights, which are tied into that kill switch for power, kept blinking. I never even noticed the lights on the indicators. He wants a set of the indicators I have, so makes sense he was drooling over them. Bypassed the switch engine fired not even a stumble as of yet. Just ran it on the hose, but it sounds good so far. Pulled the switch apart and corrosion inside. It will show 12 volts across it but as soon as you put any type of load, even a bulb, it flickers after the bulb warms up. Just like my engine. My kill switches look like the sierra ones, I'm changing them over to the aircraft style with the up/down toggle. I don't have the room for the mercs. Thank-you to everyone for the suggestions, can't believe it was the basics, that get me everytime.

Thanks for the update. AND STILL can NOT believe you never had an issue at full throttle but did below that setting on the exact same runs. That was the big throw off.

On MPI / TBI engines it is not a good idea to pipe in other 12 v add on sources into the ECM harness, Key switch wiring, kill switch wiring or the main engine harnesses. The marine OEMS totally advise not doing so especially Mercruiser, Just saying.

The only thing I can think of was that the engine was spinning fast enough to keep running even if it lost power for a split second but then again there wasn't any alarm, well until it bonces off the limiter, but anyways..Plus at that speed I wasn't really watching the trim tab lights during the day. I can't believe all the taps there are under the dash going nowhere or to accessories. The kill switches are what sunsation put in I'm guessing. I'm going to change it over to a relay set up with toggle switches controlling the relays. The joys of buying used, but now I have a reason to clean it all up and rewire correctly. Thanks, Happy Boating!!