Well as supected,the in-tank hose was kaput and that seems to help with the bucking/lurching but car is now sputtering below 3,500 RPM and miraculously smooths out and has lots of pep from 3,500 up.Runs like crap when cold and takes a VERY delicate touch on the throttle to get it warmed up without stalling.Below 3,500 RPM there is also a lot of sputtering and a choking internal backfire sound occasionally..We recently replaced the thermo-time switch and removed the airbox thermostat assembly with accompanying aluminum hose as this was designed for Sweden...Any suggestions?

Now that the hose is fixed (told you with confidence because I've BTDT with a 79 GT) you need a CPR, I think. Very common K-jet fault in a 20 year old car. New one's are $250 which sends me to the yard looking for clean shiny (recently replaced?) ones. There are several types so go by year and look carefully at what you have to match it. I.e., no vacuum hose tubes like the turbo ones.