TBI 454 Silverado with a miss...help?

[medually]

Hi
Being a convert to Detroit heavy metal....Silverado C3500 Crew Cab 1988 454 TBI I have to admit it is hard to find someone down my part of the world that knows anything about TBI systems. I have replaced all igniton components, new fuel filter, K&N air filter, new MAP sensor, new O2 sensor in the exhaust (dougs headers) etc. It has a miss at light throttle openings and feels a bit flat and my mechanic has tried more timing to give a bit more get up and go but we then have issues with pinging which got a bit better running 98octane but at the equivalent of $5.60 a US gallon it is getting pricey
As far as I know it has stock cam etc and has done around 96000 miles and is CA smog vehicle

Does anyone know of a replacment TBI assy or efi that is cost effective and will allow custom programming etc or having experienced the same problem come up with a solution?

[dumbucket1]

Does it have an egr valve? My 91 did the same exact thing. Unplug the vacuum line to the egr valve and plug it. now take it for a test drive and see if it clears up.

[Lt.Del]

you've replaced all ignition parts, so, I'd gear towards gas.
My 91 tbi had a bad miss and I swore it was a timing issue or distributor.  It turned out to be the TBI itself. There are two plastic parts connected to wires at the top of the throttle body. One controls the left side, the other the right side....at idle you can see fuel going into the throttle body.

I was looking for the problem one day when i notice one of the plastic parts with wires not telling the gas to enter the throttle body, only one side had gas going into it.   I pushed on the plastic clip thing and it activated it gas started pouring back into the body as it should. I let off my pressure and it stopped again.  I went to the salvage yard and yanked some of those clips off other TBI units and wired one in place of the messed up one and she's been purring ever since.   

[medually]

hey thanks guys will give those couple of things a try

[medually]

tried the plastic clips....firing fuel into both carby throats...I know the mechanic did check the EGR valve as well

[VileZambonie]

Check the TPS