Odd high idle

1989 Gms Z71 4x4 5.7 Automatic.
Turns over a lot before start when cold, occasional puff of fuel smoke from tailpipe when it starts. Idle doesn't come down until driven for about 10 minutes even on hot summer day. If shut off after driving then restarted quickly, idles good, if off for 20 minutes or more idle goes high again until driven a few mins. No trouble codes, new IAC valve, oxygen sensor, distributor shaft, temp. Sensor, no intake leaks.