Engine Performance problem
1998 GMC Sonoma 4 cyl Two Wheel Drive Manual 205000 miles

I have a high milage 98 S10 with a manual 5 speed. A few weeks ago I had trouble accelerating from idle. The engine would misfire and the truck would shudder in 1st from a stop. I pulled over and manually moved the throttle under the hood, problem continued. I turned the truck off and let it cool off. It ran fine after that. Figured it might of been a little bad gas. Then today I was driving and I looked down at the gauges to see the voltage meter dancing. Few miles later the truck stalled and all guages dropped to zero and back up again. I pulled over and turned the truck off. Started again and continued home. I checked battery connections, oil, fuel and filters. All seem to be fine. Please help before I get stranded....