Is the transmission in a 95 sierra with 4.3 liter vortec comapatible 5.0 v8?

No, the transmission in a 95 Sierra with a 4.3 liter Vortec engine is not compatible with a 5.0 V8 engine. The 4.3 liter Vortec engine has a different bell housing pattern than the 5.0 V8 engine, so the transmission would not be able to bolt up to the engine. Additionally, the transmission in the 95 Sierra is not strong enough to handle the power of a 5.0 V8 engine.