suburban furnace tripping on high temp

I am using the gauge port on the regulator.

I do not believe I have a pressure problem. My "thinking" is that my old regulator may have been giving low pressure (below 10.5 at the furnace).

This may have masked a problem that may have been there for years.

I got the part number for the switch from the factory.

For an SF-35Q, I got a 232504.

I believe it is set to 160 deg F.

The problem appeared with the factory switch ... my second switch and I just changed it out again ... we well see what happens.

I need to go out and get another thermometer ... my IR died last night (said the burner was over 1000 ... and snow (and rv walls ... thermostat said 32) was 3.4 deg F.

I should have said, I am an instrument tech ... worked at a refinery and a nuclear rod plant.

This one just has me scratching my head.

I am just dressing up to go re-install the furnace (falling to single digit cold tonight).

I will time the off / on cycles .... my best guess today with the new duct is about 5 maybe 8 m in on .... less than a minute off.

I can't help but thing it must be an air flow problem. My thinking .... with just an open hole on the back of the furnace (middle port so you can see part of the high temp switch) it runs and does not over temp.

Even putting on just 6 ft of straight hard pipe and 4 elbows (just aimed it outside so there would be no other restriction) it over temped!

I just made a plug for the other holes (never pushed out). I am thinking maybe letting some air out from the hole right next to the temp switch on the other side.

I also just relocated the board so it no longer blocks any of the air intake into the blower.

I will let you guys know how I make out!

I really appreciate all the advice and input!!!!!!!!!

Mike