Fluctuating temp gauge - part...whatever

This past weekend, I removed the electrical temp. gauge from the head ('94 K1500 Burb. 350/4L60E) and installed a mechanical gauge in place of it. I took it for a drive and the temp went straight up to 240 upon acceleration.
This rules out the gauge or any electrical trouble.
This really ticked me off, so I did a back flush on the system by pulling the upper heater hose off the radiator, removed the thermostat, and ran the garden hose through the whole system several times until all the water ran clear (no a-frz.). Then I replaced the t-stat and drove it again.
This time, it wasn't as bad, but still got hotter than normal 220-230. Last night, I had an extra 10 minutes, so I took out the new thermostat and replaced it with one I had from a previous project that had a 1/8" hole drilled in the flange. Took it for a drive and it took a while to warm up, but when FULLY warm, it ranged from 175-185 deg. and would move up to 190-193 upon a normal acceleration. Never warmer than this, though.
A few questions 1) Is 175-185 warm enough for a full operating temperature? Both the new and the drilled t-stat are 195, which means "full open" at 195, right?
2) If I leave the drilled t-stat in, my problem symptoms go away, but am I just masking a real problem that will raise it's head later on? I should be able to run the factory t-stat as the factory designed it. It worked that way for 10 years, so no reason it should stop today.
3) I've got an apointment with a guy I really put quite a bit of faith in when it comes to vehicles tomorrow. Should I just bite the bullet and let him handle this, or should I just keep throwing time and money at this thing? I guess what I am asking is "can anyone else offer up any suggestions before I take it to someone?"
Thanks to those who have offered that tip on the drilled t-stat. I already had one like that, but you guys persuaded me to install it. Thanks! Only trouble is what I stated in my second question.
Thanks, Snowman
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Just a guess, Is the timing correct. too far advanced timing can cause it to get hot. "Snowman" <somethingorotherdotcom> wrote in message

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