codes everywhere

[ZGHOE05]

hey there guys just joined thought id post my expirence with my 05 Z-71 tahoe. started by cranking and not starting , no check engine light or anything , mechanic didnt know so he charged me 80 bucks and sent the truck which he had gotten to start home with me , it did fine for 2 days . then it wouldnt start , finall got a CEL ant it was p0335 crankshaft position sensor 50 sollar part changed it one weekend and started it to find it started great but ran like shit . i thought this was due to not doing the releran process, it spit and sputtered and shook under any throttle, scaned it and got p0336 another crankshaft position sensor code , replaced the new sensor with an ac delco sensor 90 dollar part and relearned it and it did great , now im throwing a p0420 and p0430 code and im planning on purchasing 4 new o2 sensors and the new bolt in catalytic converters .

so my question is how hard is the install going to be on the bolt in cats , ie: what do i have to remove to get to the flange bolts