Can’t figure out acceleration noise and more!

[mamma03]

Hello, I have a 2011 Expy Max that I purchased almost a year ago. I have poured money into this beast and I am struggling to find the current issue. I have had it looked at by 3 mechanics who all have said different things, and the issue still has not been solved. The engine makes such an awful growl when it starts. It gets better if used a few times during the day. Sometimes, starting it up takes longer than it should. It has louder acceleration noise, it almost sounds dry. I will barely touch the gas and it sounds like I am putting it to the floor. The acceleration is crappy, I have poor fuel mileage, it’s jerky on acceleration or braking. So far it has had spark plugs done, the ring gear replaced, belts, etc. it has had regular upkeep. Each mechanic says one thing or another, but still insist there is no problem that can be found. Has had several diagnostics run on it, it has never thrown a code. The problem has been present for about 6 months. I have to take it for a long road trip in a few days and I am terrified it’s going to die on me. What can be wrong with it? Would you trust the word of the mechanics? One said it was the timing chain, but after investigating, he didn’t think it was the issue anymore and that replacing the spark plugs would solve the problem. The other two said they found absolutely no issues and that the noise it makes was it’s usual..but it most definitely is not.