GTV6 start/run problems

I need some advice about my 1984 GTV6 starting/running issues. When attempting to start from cold one of three thing occurs.

1. Starts and runs fine.

2. Starts and runs for a minute or two, engine speed begins to slow down, stalls, will not restart.

3. Cranks fine , does not start.

I am never sure which situation I will find, but #s 3 or 2 are becoming most common.

Any suggestions? Where to start?

Thanks in advance,

George