Chevrolet S10 Boost Pressure Actuator Issue

Sounds like you're on the right track. A faulty boost pressure actuator or the valve it controls can definitely cause those symptoms. The whistling and hissing are classic signs of a boost leak. Reduced power, stalling, and bad fuel economy all point to the engine not getting the right air-fuel mixture due to the boost issue. Have you checked for any obvious signs of damage or loose connections around the turbo and its associated hoses?

I've visually inspected the hoses and connections, but nothing jumps out. Could you elaborate on specific areas I should focus on, or any particular tests I could perform to further isolate the issue? I'm reasonably handy with tools, but my diagnostic skills are somewhat limited.

Since you've done a visual check, next step would be to see if the actuator rod is moving freely when the engine is revved. If it's stuck or sluggish, that's a strong indicator of a faulty actuator or a vacuum issue. Without proper diagnostic tools, it's tough to pinpoint the exact cause. Considering the symptoms, and if you're not seeing anything obvious, it really would be a good idea to get it to a workshop. They can properly test the boost system and pinpoint the problem before you start throwing parts at it.

I took my S10 to a trusted workshop. As you suspected, the boost pressure actuator was indeed faulty, specifically, the electrical bypass valve had failed. The total repair cost came to around 250€. It is running smoothly now.