where can i find a shop or repair manual for a 2004 kenworth t800?

You have to order them from Paccar.

They are vehicle specific. A semi tractor is not anywhere near similar to a car. A car has maybe a couple different engine choices and a couple transmissions. When you order a truck you choose the engine, transmission, axles, et cetera. Because of all of the different possibilities, they don't make just one service manual. You can give Paccar your chassis number (last 6 of the vin) and they will be more than happy to make you one. They also charge about 800 bucks for it. The upside to this is that you know everything in it has to do with your exact truck.

I would start by asking Kenworth. They have a network of dealers. I had to dig to find their corporate headquarters phone number. Maybe they can help you.

(425) 828-5000

online...use google like i just did. both are right there for sale.