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Could be an inline fuse break or ground issue.
Escapes have trouble with the door switches. Try removing it and use an electrical parts cleaner on it and reinstall. If it works better then the switch was either dirty or the contacts are going bad and the unit will need replaced. If the window sometimes works fine, as you said, I would lean toward the switch.
Does it overheat? If so, replace thermostat or check coolant level. Need to know temp. of engine at stall and what it does when it stalls.
Need more info. Very likely it is wheel bearings but, after sitting so long the tires themselves could be causing the noise from 'flatsiding' and cracking from weather. Have bearings checked first due to vechicle age. Other possibility is a CV joint could be going bad but not as likely.
Get the head gasket replaced as long as there are no other leaks. This should take care of the problem. Shop around for prices. Coolant in the oil is the telltale sign of head gasket failure.
Monitor your engine coolant level very closely. This sounds like the early stages of head gasket failure or valve gasket failure as well. Check spark plugs to make sure they are dry with no 'pools' of oil in with the plugs.
Most common cause is a failed oil pan gasket that needs replaced. Other causes are, oil pan plug missing or poor condition gasket. Improperly seated oil filter. Check these and see if 1 of them is the cause.
Maybe a little high but if labor is already included, it is not ridiculous. Call around and look for a $4500 price with labor included. Here is replacement engine costs: http://www.autozone.com/autozone/parts/2000-Chevrolet-Impala/Engine/_/N-jdz5uZ9enw6?filterByKeyWord=engine&fromString=search
Probably about $1100 dollars
This should cover the procedure for you http://www.ehow.co.uk/how_7323646_replace-fuel-filter-duramax-2500hd.html