Just hard to believe there was that much CRAP in the motor to start with. New oils are all Detergent and don't let CRAP buildup in the motor...... unless the previous owner NEVER changed the oil and just added a quart every 4 months.


You didn't say the year or if 4 x 4.... how hard to pull the pan off ?
Getting warm and draining would be a good first step

 

Maybe it's 30W oil instead of 5W-30. The cold temperature will make 30W oil seem very thick like you've described.

 

Better just drop the pan and scoop the goop out of their.
And be sure the oil pump pickup is clear.

 

Here is what I did. 3 consecutive oil changes. The first two i ran it till operating temp. The first 2 the oil came out blacker than black. On the 3rd one it ran for 30 mins, drained the oil and it was its normal color. So I will put refill with more oil and another new filter. Engine sounds fine and never lost pressure during this process.
Lesson learned... NEVER let a mechanic talk you into and oil flush!!. Hopefully the engine is saved

 

Then run 1 quart of marvel m oil with new oil . . At 305 let her run til she croakes.

 

Stop putting CRAP in the motor oil. It is formulated to do a PERFECT job of lube. You don't need a "FLUSH" and you don't need "marvel Majic" .......... It is possible that the FLUSH you added had some CHEMICAL REACTION with some additive package in the oil and caused the CRAP to develop.......


Years ago I worked on a dozer final drive that was "FULL OF CRAP".... sent the oil in for analyses and they said the original 80 w 90 gear lube was removed and someone had refilled it with 15 w 40 MOTOR oil and the addative packages COMBINED to make "jello".

 

Seems pretty clear that the oil treatment used by the mechanic reacted to the old oil in a bad way and nearly ruined your engine - I wonder if one of the four stages had anything to do with 'stop-leak' - sure sounds like that's what gelled-up and plugged the oil pick-up. Its a damn good thing you pay attention.
Personally I wouldn't hesitate to use a solvent before an oil change, and on one GMC van I had years ago that was lightly driven, valves would stick a little every so often. I was buying 'Kreen' at that time from Kano Labs (the maker of 'Kroil') which is a very strong internal engine cleaner, and I would put in a small dose which de-gummed the valve stems and kept it running sweet. It is so strong that if you use the full amount, 16 oz or 32 oz, it even dissolves the carbon around all the gaskets. I remember using it in a used '65 Mustang I had bought for $500 (1972) and watching black 'ink' come out from under the valve covers and run down the block. That engine was severely 'coked-up' with baked-on carbon but I managed to drive it until 12/1975 when I traded it in on a brand new 1976 Trans-Am (400, 4V, 4-speed, posi).
In typical fashion, many here will react violently to the thought of putting a solvent in an engine or even changing the oil in an automatic transmission. There are ways to do things and not harm anything, and there are wrong ways to do things. This doesn't make normal maintenance procedures 'bad'. This is superstition at it's worse.