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Running very small amounts of propane and having your chip properly tuned for it will be ok for your truck. However, if you are wanting to use it as a power adder, forget it. Your 2002 has PMR's, and propane as a power adder will quickly send a rod through your block.
Just remember that propane is a fuel and will combust. It is not injected directly into the combustion chamber as diesel fuel is. So as the propane is compressed, there is the likelyhood that it will pre-detonate. As with any engine, gas or diesel, early detonation = bad news.
Those who are using propane successfully are doing so in extreme moderation and use it as nothing more than to gain a bit of mileage. There have been folks on this board and others in the past who have played with pane as a power adder, and have posted the devestation aftermath.
The actual economic viability of using propane as a mileage gainer also depends on the cost of the propane. The rule of thumb I've read is that the break even point is when the cost of the propane is equal to or slightly less than the cost of diesel. I've also seen a post very recently where one guy said that he was able to get a substantial price reduction on his propane refills since it was technically being classified and run as "automotive fuel" (I'm talking something like noticeably less than $2 per gallon).