p0300, p0304, torque converter not locking sometimes, replaced many items, any ideas?

[syclone01]

1998 Tahoe 4wd, 180k miles. Truck at part throttle and mainly under any small load such as pulling small boat or going up hill/bridge will shudder/misfire. I'm getting po304, p0300 codes. I have replaced the lower intake gaskets, MPFI upgrade, new Delphi fuel pump and filter, new Delco cap/rotor, wires, delco 41-993 plugs. I ordered and waiting for a new crank sensor and delco coil, after I install those and if not fixed was going to order a new GM distributor. I have also noticed the torque converter is not locking up when it should, flat road at cruise 65-70 and it's not locked up, sometimes it will lock. My coolant temp thru my scanner reads 192-194 on a 75deg day. I've sprayed carb cleaner around intake/mpfi oring area and got nothing. I cleaned the MAF as well and noticed nothing. When I go WOT I see my number 1 oxygen sensors on both banks show right at .87 so it seems it's getting fuel at wot. Any ideas on where to look, I've googled this and I seem to have replaced most of the items that caused this problem for most but I haven't found the problem yet. Thanks for any suggestions.

 

[FL-Bowtie]

Could be torque converter lockup selenoid. Its basically an electric valve in the transmission that controls the lockup. A good trans shop can check, the part is cheap but the daignostic not so much.

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[twomanymontes]

The computer delays Torque convertor lockup if there is a misfire issue, so that is normal. The convertor would amplify the misfire. If you have already swapped out all those parts and it still has a misfire on #4 cylinder, you might have an internal issue. Possibly a valve hanging open. Best thing to so is a leak down test as well as a compression test. Compare it to the cylinders.