I did not end up pulling the EGR tube back off, I did however, replace every vacuum hose other than the booster (which was connected and in good shape, but anything is possible). Also, as time allowed over the weekend, I pulled the fuel rail back off, replaced the injector o-rings with the ones that came with the LIM gasket kit (really didn't think I needed to originally, as the ones on there now are about a month old), and re-seated the fuel rails with fresh grease on the o-rings. Took care of a couple of other, unrelated repairs while I was at it (water pump, VC gaskets), but everything back together, cleaning everything I took off before putting it back on, and BAM! issue resolved! I'm guessing it was the FI o- rings that were the culprit, so it seems it's a good idea to replace them every time I take the rail off, regardless of how old they are.