Code P0301 and Ocassional P0171

[torqlox]

Well, my 2000 Sport OHV has been acting up since I replaced the upper intake gaskets, DPFE, IAC, and EGR valves & hoses. Before these replacements, the truck was giving off a P0171 (Lean Bank One) code which is a common problem with leaky plenum gaskets on these trucks. The problem is that now it's throwing a P0301 (Cylinder #1 misfire), and I can't seem to detect the root of the problem.

Parts replaced within the last 6 months:
Both upstream O2 Sensors
Plugs & Wires
Coil Pack
IAC Valve
EGR Valve
DPFE Switch & hoses
Fuel Rail Gasket
Upper Plenum Gasket

I have not replaced the very lowest intake manifold gasket yet, but then again I have not heard any "sucking" sounds indicating any violent vacuum leaks. Injectors were cleaned and pulse tested well. Any ideas on where to go from here???

 

[torqlox]

UPDATE: the hose that goes from under the throttle body (Evap return hose I believe) was completely collapsed and cracked all over. In an effort to start ruling out possibilities and weed out the false alarms, I replaced the entire assembly with tough 3/4 transmission cooler return line hose. The engine runs a tad better, but still getting a P0301 Cylinder #1 misfire. Also, I thought I might add that on my torque app, I read full activity on O2 sensor bank 2 sensor 1, but zero activity on bank 1 sensor 1. Still not sure if that is just my app that is not reading it or not, but I am going to troubleshoot further tonight.

 

[torqlox]

Well, I pulled the lower IM, and found the Gasket to be in pretty bad condition, as well as the intake runners being overrun with gunk. I cleaned everything up and bought a gasket. There were no detectable vaccum leaks from the spray test, but I have seen a lot of people with misfire problems due to the lower IM gasket. Can anyone tell me if this could of been my case by the following pictures?

Before:

After:

 

[superfly_1]

did you ever figure it out ? i'm on the same boat without paddles