99-02 All had the 7.3 in them. Yes 2000-2002 and some 2003 trucks have the PMR rods, while the earlier ones have the forged rods....Dont worry about that unless you plan on going over 400 hp with it. If you just want reliability, and possibly a few things like chip, intake, and exhaust, you cant beat the 7.3.....
Heres a few questions....
How many miles are on the truck?
Is it on its original Tranny?
What did the previous owner use it for?
Are there any leaks?
The most common problem with these trucks, would have to be oil leaks....Mainly things like the IPR sticking, the ICP going bad......If the valley of the engine is dry, and it idles correctly, chances are your in good shape. If the valley is wet, or oil is dripping under the truck, or if it looks like it has a main seal leak, it has a leak somewhere on the top of the engine, which can sometimes be a PITA to figure out.