Why does my Tahoe not want to start, but runs good once it is started.

So, it cranks and cranks without starting? Often times you may have good fuel pressure but an overabundance (or possibly lack of) air getting into the engine. When this happens, it could seemingly "flood" the engine when fuel keeps coming but ignition doesn't happen. You could also have an ignition / spark system issue. Troubleshooting hands on is required to determine what is happening.