Small Engines (Lawn Mowers, etc.): Yard Machine 46 cut , 18.5 hp Briggs and Stratton: No get up and go!!, briggs and stratton, hp briggs

Question
I am at my wit's end, with this Yard Machine, I just recently  had sunk a short block into it and it has no power. In the 7 speeds that it has it will only run in #6 and then very poorly on flat ground and the only way to get it to go uphill on a slight upgrade is that it will come to a stop and then if you put it in low gear it will run and once it rolls you can put it back in Forward and it will take off slowly and then increase in speed, but it moves more like it is in the 3rd or 4th speed and most certainly not 6.
The blades engage good and the belts seem somewhat lose (can insert finger behind them, but the main thing is that it just seems to slow down if there is the slightest grade, and overall does not move like it once did. There is no speed at all. I hope that you can give me some advice or insight into what might be wrong. It is doing exactly what it was doing before I took it into Buccheits to have the new short block put on it. The performance is terrible. Please Help!!! Thank you. PS. It does appear to be getting overly hot and then has that smell of hot oil spilled on an engine? I commend you for having this free service, this is just what a lot of us, need when it comes to lawn equipment, Thank You  

Answer
If you just had a short block installed and you have the same problem, take it back to the shop that did the work.  If they didn't test it out and let you know something else was wrong or didn't correct something they should have, it shouldn't be up to you to try and fix it.  Hope this helps.