I have a 1994 mazda b3000. I changed the oil and thermostat and now when I start my truck cold, it does fine for 20 or so seconds then acts like its starving for fuel. Then I feather the gas and drive away. After a couple of minutes driving, the problem is gone. Idles fine at stops. Any ideas?

Replace the Engine Coolant Temperature (ECT) Sensor, which affects fuel injector pulse width. The ECT Sensor is a temperature dependent resistor (thermistor), whose resistance decreases as the engine coolant temperature increases. It provides a richer mixture when cold, leaner mixture when hot. They become corroded, due to not changing the coolant frequently enough, flood the engine, and waste a tremendous amount of fuel.

Ensure you installed the correct temperature rating thermostat (OEM) for your truck and that you installed it correctly.

It might be time to have the throttle body inspected and cleaned as necessary. Maybe the injectors, too.