Crawford

Hey guys I'm having trouble with my 82 C10 305 3 speed on the column. When starting out in 1st gear going straight it has no issue. But when starting out turning (like at a red light or stop sign) it feels like ive tried to start out in 2nd. it has no power and tries to go dead and jerks like if I've dumped the clutch. I did not notice this at all last week and then I put a can of Seafoam in 2-3 days ago and now its doing it every time. I changed the fuel filter yesterday and today I ran out of time changing spark plugs before work but it does have the front 6 plugs replaced ill change the other 2 in the morning. any help would be greatly appreciated thanks