truck stumbles at about 3800-4000 rpm- then straightens out

1500 silverado 350 5 spd- no scan codes- repl. wires, plugs, TPS, TBI clean, subbed coil. Could be fuel pump ??? changed filter 2x in 4 months. Help. Try, just for testing purposes, unhooking the EGR valve and seeing if that makes any difference at all. If not, you are probably looking at an electronic problem either with the distributor's pick up coil or the Engine Control Unit itself.
Is the ign. timing adjusted correctly? You have to disconnect the Spout Connector to adjust it correctly or the ECM still has control. I really think if it were the fuel pump, the harder you run it, the more likely it would starve and cut out. Pumps can do strange things sometimes.
Mr. GT