Hi DJ,
My 89 3.0 is having the same exact problem....if you let it sit for more than a day it is very difficult to start. Once it's running it runs fine, temps aok and will fire right up all day long.....unless you let it sit for more than a day!

I did replace the engine coolant temp sensor and that did not make much difference, did not solve the problem! My engine is OEM and only has 120,000 miles...so not a mileage issue.....I'm up in Lake Tahoe in the snow and cold...and that doesn't help. This does not happen in the summer/dry months.

Just FYI: I have replaced timing belt, water pump, thermostat and engine coolant temp sensor. Engine passed Block test and compression test aok.

Would a bad check valve look like having to crank the engine/bump the starter 10-20 times to get the fuel to the engine? If it's a bad check valve why would it finally start at all??...and then run fine???