No, nothing whatsoever.
The 2003 GMC Envoy inline 6 engine does not have a timing belt but a timing chain. No need to replace anything unless the chain breaks.
There are several. Anything newer than 2007 will typically employ a timing chain instead.
timing chain timing chain
Timing Chain
The 4 cylinder has a timing chain but the V6 has a timing belt. The belt on the V6 must be replaced at 110,000 miles or 10 years whichever comes first. No maintenance is required on the 4 cylinder chain.
timing chain timing chain
timing chain timing chain
No Belt=It has a Timing Chain.=
You do not have to do anything. It is recommended on some vehicles, but not many. Timing chains usually last the life of the engine with no maintenance.
It has a timing chain
Timing chain
It has a timing chain.