2006 vw jetta 2.5

If it is the upstream O2 (pre cat) and it doesn't work, then yes it will affect your fuel ratio (or fuel supply), but if you can't shift past 3rd gear, you may have a separate issue. Could be a huge range of problems, maybe your ABS module, transmission speed sensor, etc. You need to take it to a mechanic, brother.

if your losing power, FIRST thing I'd do is cheapest parts. I'd replace my spark plugs and wires ( you're supposed to this every 18 months anyways). if you have shift or gear issues, you probably have a dry gear box and need to get to a garage who can do a PMI on your bands. Get'r oiled up. this is all general maintenance things. Cars are like babies, we are always putting money into them and staying on top of things so they can keep rolling. good luck from Utah. BTW, I'd LOVE to have a 6 speed here in the mountains of Ogden, Utah!!