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[girlmark]

the 7.3 Powerstroke is one of the best engines in recent years, shouldn't have any issues with biodiesel other than gelling in cold weather. The best way to prevent gelling is to familiarise yourself with cold testing- take a sample, put it into a small jar, and freeze it. The temp at which it starts to look cloudy is the temp at which it may clog filters (the clouds are small frozen crystals of biodiesel).

To deal with gelling issues, you can get a filter heater that increases the range of temperatures at which you can run the fuel, you can blend a lot more diesel in in the winter, you can use zero biodiesel in the winter, or you can try some other modifications. If your fuel is made by the producer out of animal fats, poultry fat (really common source these days), palm oil, or some other fats, then the cold filter plugging point will be worse than if it were made out of soy, corn, canola, or other 'liquid' oils (the fats biodiesel is fine in summer and it has some other advantages (higher cetane for instance) over liquid oils, but they're not big enough to worry about in warm weather).

I'm not sure which 7.3 you have:

The 7.3 Powersmoke does well on SVO with an SVO conversion also. It's one of the most stable old truck diesels for SVO conversion. Hold on to this truck, I wish I had one instead of a GMC right now.

The 7.3 IDI has a couple of issues:
-works fine on biodiesle other than the same gelling issues (same solutions apply, in fact, one of my old 6.9's had a built-in 12V fuel preheater right before the filter and I never gelled in a mild climate where our winter only hit 40's whereas some other users did experience cold filter plugging)
-for SVO conversion they're more finicky., They had the crappy Stanodyne injection pump that doens't like SVO's higher viscosity and occasionally seizes in that application. I'd be prepared to replace pumps and be very careful about SVO conversion and monitoring of system temperatures if I were trying to convert one of these to SVO.