Diagnosing po171 and po174 for 1998 GMC Jimmy

All that data shows you is what you already know. The system is very lean for some reason. You need to start out monitoring the fuel pressure with an accurate gauge and check it very thoroughly for any vacuum leaks or leaks in the intake snorkel. The fuel pressure can never go below 55PSI and should max out near 66PSI under acceleration.

I blew cigar smoke into booster hose to see where smoke might come from. I see smoke come from air intake tube/resonator. Is this normal?

You're been watching too many Scotty Kilmer videos. You'll get sick attempting to blow enough cigar smoke to find a vacuum leak. Of course air will leak out the throttle body. That is the air intake point and would have to be sealed off in a real smoke test, although any real air leak in the snorkel between the throttle body and the MAF will cause lean codes.

Thanks, I will try with one of those $29 smoke machines off ebay.

$29???
You want to be very careful. The EVAP system can only deal very small amounts of pressure. I paid $1300.00 for my smoke machine because it has very precise pressure measurements.