I owned a 4020 gas powershift about 20 years ago. It was a great tractor, but, as others have said it was bit "thirsty" even for utility work. But in some sense, the gas consumption issue was both a curse and a blessing. Pulling a 4020 gas hard would take up to about 8 gallons of gas per hour compared to probably 5 1/2 for the diesel. So it didn't take too long for the gas tractors to be pulled off the hard work and delegated to some less demanding tasks. Consequently, the 4020 gas tractors have much lower price on the used tractor market so they are easier to purchase. Of course, when you sell it, it doesn't bring nearly what the diesel tractor would.
If you look for used 4020 tractors, or a 4010, there aren't a lot of gas models to be found. The one I bought was in really nice shape and was priced about $3,000 less than a diesel with similar hours, condition, etc. Of course when I traded it I got less money than had it been a diesel.
As I looked around for tractors it also seemed that the gas tractors looked like they had lead a more "gentle" life than diesel tractors. If they were a loader tractor all of their life they could look rough but I think the high gasoline consumption put a lot of them performing work that required less of hard pull all day long.
I wouldn't hesitate to get another 4020 gas tractor. And with the powershift transmission you can't find a nicer tractor for utility work. Like any gasoline burning tractor of the day the carburetor condition is critical to the performance. I had some issues early on with my 4020 but actually ended up putting a new Zenith carburetor on replacing the original Marvel Schebler carburetor. It was a little rough running at cold start up but smoothed out quickly.
If someone is just looking for a 90 hp tractor for some general utility work with the occasional tillage use then the higher gasoline consumption shouldn't scare them away in my opinion. Just accept the fact that it won't be as easy to re-sell as a diesel and you have a little higher operating cost.
