Engine Needs To Be Replaced
 

I was driving on the highway and then I felt like I was on rough road, engine light came on and I lost a lot of power. Pulled off highway and truck died. Took it to mechanic and he said one of the cylinders is blown and only way is to either take it to a testing place to determine which one and what needs fixing exactly or replace the engine. Taking it to the testing place is most expensive and to replace engine is about $3000 with 90 day warranty and about 100,000 miles on it and about $1500 for labor.

I have personally fixed my air conditioner and other repairs but this is a whole different level. I would like fix it myself and I have the space at my house to do so but it is what I imagine an advanced level job.

Has anyone pulled their engine and fixed it, or had the same issue or any advice, thoughts?

Welcome to HF.

What Hummer are you asking about? Year, model and miles should always be provided.

Not sure if you misunderstood what the "mechanic" was trying to tell you, but if a "cylinder is blown" you would need a replacement if I even understand what that is supposed to mean (ie. cracked or damaged cylinder wall).
If you have a cylinder without compression, you could have a bad valve, rocker or valve spring, which requires a rebuild of the top (cylinder head) of the engine, not a replacement.

So as far as had the same issue, I have no idea what issue you have.

I just called the mechanic and he said "Internal failure cylinder #4. He won't know what exactly is going on until it is taken to the machine shop. Most likely something inside cylinder head that is a common problem (usually top part of the engine).

Hummer H3 2007 and about 140,000 miles