This sounds like a bad catalytic converter or resonator in the exhaust system.
2 months ago. whens the last time you changed your fuel filter?
the simple answer is the coolant fluid - make sure it's full where it's marked, after driving it ten miles. the bigger problem is unlikely if it runs alright, so try the first. you might just need to flush and fill the coolant too..
It could have an engine problem
Bad wheel bearing? Brake pads worn?
TroLLiNLOLOLOLOLOLOL
injectors are a common problem
acid precipation
Pollution.
Its a design problem. Ideally there shouldn't be.
If there is no trouble while shifting, then the problem most likely is with the ignition sequence. This could be caused by bad gasoline, a bad timing assembly or faulty spark plugs/wires.
I have a 97 with 170000 miles. had the same problem. it was the WATER PUMP, the finns wore off!
When a 1999 S10 is sluggish and surging with going up hills, perhaps there is a problem with the transmission. The filter might need to be changed, more fluid added, or it might need a complete overhaul.