5.7 TBI throttle response

[Krosati]

The Suburban I bought a couple of months ago seems to be sluggish from take off. I had some problems with the charging system but I had the alternator converted to SE and it charges fine now. After spending a few weeks driving it, I find that gas milage is only 7.33 MPG!
In order to rectify this, I started checking the manual for possible causes.
Here's are the symptoms:
1. When cold, truck drives great and throttle works smooth from idle to 70 MPH.
2. Once warm (not fully up to operating temp),idles fine but starts from dead stop are sluggish unless at least 1/2 throttle.
3. Once fully warm, idle seems to vary a 100-200 rpms and starting from a stop (sometimes) causes the engine to die.

Here's what I have done so far:
1. Cleared codes (none present but did it anyway) I do not have any new codes stored in the ECM.
2. Confirmed open loop on cold engine
3. Confirmed open loop at idle and closed loop above 500 rpm on warm engine.
4. Replaced temp sending unit (on front of manifold near t-stat).
5. Replaced t-stat with 195 degree unit. Spring side is in manifold.
6. Replaced O2 sensor
7. Replaced TPS. It is a non adjustable TPS.
8. Removed air cleaner to observe the fuel spray in TBI. There seems to be a few droplets every few seconds but mostly just a fine mist. Purchased injector cleaner and added to full tank. Still running last half of this tank so milage may increase a bit.

Any ideas as to what to check next? I am replacing the fuel filter and spark plugs Sunday to see if this helps.