1999 Silverado Stumbles

I have a 1999 Chevy Silverado 4x4 with 64k miles, 5.3 L engine and automatic tranny. The truck "stumbles" at different times. The problem generally occurs when I first start the engine and put in gear.
Once I begin to give it more throttle, the problem starts to dissipate. During acceleration at low rpm and slight throttle it also stumbles/bucks. The truck seems low on power in overdrive but when it kicks down, it seems to be ok. I have changes plugs and fuel filter. No trouble codes or check engine light. The dealer was unable to find anything wrong...it was working well when I took it in. Any Ideas? I can recreate the problem by holding the brake and throttle, loading the engine. Mostly this is noticed under 1500 rpm.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
A comprehensive scan should show something in the lt/st fuel trim, or misfire counts, possible egr not closing completely, lots of possibilites. Someone has to have the patience, tools and know how to dig into this.

-
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Motorsforum.com is a website by car enthusiasts for car enthusiasts. It is not affiliated with any of the car or spare part manufacturers or car dealers discussed here. All logos and trade names are the property of their respective owners.