She's not running well..

[Fourspeedwagon]

I didn't drive it last year because of the leaky axle boots. Last fall I put a couple gallons of premium and some octane boost/fuel stabilizer into it for the winter. Yesterday I changed the boots, topped the transaxle and as long as I was under it I decided to change the oil/filter too. It took a several spins to get going (not unexpectedly). Now she idles OK and doesn't need to have me working the pedal, but when I went to drive it back into the shop it's very boggy and doesn't want to rev. Backfired a couple times but not a lot. Think I'm just suffering from "modern" fuel that is half a year old or maybe out of time? Seemed strange that it would idle but not rev, I was wondering if maybe the advance is working properly- But I'm not certain how to troubleshoot that. Any thoughts? Thanks- Greg
I attached a (very dusty)pic from a couple years ago (cause everybody likes pictures)