DRIVER SIDE radiator end of engine is number 1 then 3 then 5 then 7.
PASSENGER SIDE radiator end of engine is 2 then 4 then 6 then 8.

Your 4.8L isn't one coil per spark plug? It won't matter if that is so, the cables are too short to mess them up.

If it still has a distributor, the firing order will be embossed on the intake manifold. Typically GM timing on a distributor type engine is 1-8-4-3-6-5-7-2 unless you have a newer replacement cam that flips the firing order of two cylinders that is supposed to smooth the power curve of the engine out.

Now, you are talking about a 2000 GM 4.8L engine?