1991 Chevy truck hard starting

This truck has about 110,000 on it. It is not driven much. I noticed this fall and now into winter that when I cold start it, sits over night or an extended period of time, it starts hard. Almost like it's missing or fowling out. This seems to go with the outside temperature, the colder it is, the harder it starts. When it does start, it runs extremely rough, again depending on how cold the outside temperature is. It also runs rich. Within a couple of minutes, no problem, runs like a champ. Recently I replaced the egr valve, the knock sensor, gave a full tune-up and flushed the coolant system. I've also checked for vacuum leeks around the carburetor and replaced the pcv valve vacuum lines (the old one was cracked). A friend is thinking that the fuel pressure regulator is now out or going out. Is there anything else that I could look at? I've been around vehicles and not afraid to work on them, just can't figure this one out.

I now have rebuilt the fuel pressure regulator. It seems that it helped the problem out, but has not fixed it totally. What else can I look into to fix this. Thanks.

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brian
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