Need some suggestions about possible culprits and troubleshooting for a cold start problem.

Truck has a health 360 based 408ci, 10:1 CR, ported eddy heads, air-gap manifold, 228/232 @ .050 hyd roller cam, holley 780 avenger carb w/ electric choke.

Basically it started out as starting really well...and has gotten progressively worse (longer warm-up time still it's steady, etc).

Now it's at the point where it takes considerable time to fire (I use an electric fuel pump, so it should prime quickly). The first few fires are weak and barely sound like anything is happening. Once I get it to run, I have to keep it at 2000+rpm or it just simply shuts down...no stumbling, and getting back on the throttle once it's stopped firing (but engine is still turning) won't save it.

tia,
Chris