The 6.5 uses a pretty standard glow plug size, so most any diesel engine compression tester will work. Beware as I have read the $30 one from harbor freight won't work in the 6.9/7.3L, and they use the same size glow plug as the 6.2/6.5 so chances are it won't work for them either.
Let me rephrase my post. I don't think i want to pay $269. dollars for a NAPA diesel compression tester i will only use once over the next ten years.
Is there anyone willing to sell me a complete compression tester guaranteed to work on my chevy 6.5 L TD ?
Some auto parts companies have a tool loan program where you pay for the tool, use it. Then when you return it they refund your money. Our local napa store does that here.