Engine Hesitates and surges

My truck surges when at idle and has very poor fuel mileage. What can help

Truck cranks and runs, When Idling, engine surges. Gets worse when you drive it down the road. Will surge & buck after 40mph. Replaced throttle position switch, coolant sensor, distributor, cap, rotor, plugs & wires. Removed upper intake, cleaned it out. New gaskets, cleaned throttle body including EGR ports, replaced MAP sensor, and replaced fuel filter. Seemed to help for about 15 minutes, then began surging & bucking again. Any suggestions as what to try next?

Fuel pressure was 49 psi. Only code that shows is MAP sensor, which I replaced, but code still comes up. & Yes, runs same cold or warm

What diagram? & What is a TFI?

At normal idle the engine surges sometimes it stalls when in drive and foot on the brake other times it will rev way up and can barely hold it with the brakes replaced map sensor throttle positioning sensor and egr any other ideas?

Forgot to tell you have taken care of any vaccum leaks so I will check the IAC

As far as I can tell, fuel pressure to engine is ok, it seems to get plenty of fuel. Shows 39 PSI at the post on the fuel rail. (Miss typed the last one, not 49) As long as you give it gas, it runs great. Has a little miss, but once you let it idle or hold at a steady speed, it surges, & bucks like a mule.

No TFI Module on this distributor

Is the IAC cleanable or repairable?

Had Ignition module tested, passed ( cycled 25 times )
Would the IAC cause this problem? I know it might at idle, but would it cause the problem while driving as well?

Just tested IAC, it's fine. Went and had codes scanned, here is what it showed:
DTC172 ( o2 sensor fault, lean)
DTC 213 (SPOUT circuit open)
DTC 332 Insufficient EGR flow (had hose off to test EGR vacuum)
DTC 538 Insufficient RPM change during KOER
DTC 632 Overdrive trans cancel switch

we pulled the short bar out of the SPOUT wire harness, checked timing. 10BTC. Put short bar back in & checked timing again, still 10BTC.
Seriously stumped as what to check next.

While the engine is idling, it will surge or increase is rpm for approx 5 seconds, then stop for 10 seconds, then surge again. The surging stops when the heater control switch is turned off, just like an engine acts when it is low of freon in the AC. Turn the heater on, and the surging starts again.