acceptable compression range?

The compression ratio is 16.5:1 or so. I suspect you are looking for cylinder pressure, which should be well beyond testing with any reliability by common compression checking equipment....... over 2000PSI. Most diesels are measured in "bars", and need rather complex and expensive equipment to measure cylinder pressure.

If that doesn't answer your question, post more details.

I was looking at a 2500 for sale and I don't know the quality of the maintenance history. I was thinking about a compression test. Sounds like this would be a tough test to do tho.

How would you go about testing the quality of a hi-mileage 5.9 Cummins?

Wha kind of mileage does it have? Anything less than 250k and the truck should be ok as far as mileage is concerned. Its rather difficult to evaluate a Cummins without taking an oil sample for analysis, but look at the oil after having driven it for a bit. Any irregularities should be noted, such as metallic oil, or a brown color. Listen to idle quality, as that will tell you if a cylinder is not firing quite right. A diesel should be very even in its firing after warmed up. If you have access to one, take a scanner and pull codes from the truck, if there are any. Take the VIN and run it both with Dodge and the Carfax service.

Wha kind of mileage does it have? Anything less than 250k and the truck should be ok as far as mileage is concerned. Its rather difficult to evaluate a Cummins without taking an oil sample for analysis, but look at the oil after having driven it for a bit. Any irregularities should be noted, such as metallic oil, or a brown color. Listen to idle quality, as that will tell you if a cylinder is not firing quite right. A diesel should be very even in its firing after warmed up. If you have access to one, take a scanner and pull codes from the truck, if there are any. Take the VIN and run it both with Dodge and the Carfax service.