1999 Ford Explorer Help me please with my Ford explored lim

I recently had my ford explr ltd. Towed to a mechanics garage bc it wasn't running smooth, so while it was there the engine wouldn't even turn over to start so he said I needed plugs and it worked. But now I needed a new exhaust system bc my 4 converters were junk, so since he didn't have the right tools for the job I went to a professional which did all the undercarraige work " brand new muffler, converters and exhaust" so when I go to pick it up my trucks engine is jumping, stalling at everystop and turn I make and also it's smoking out of the exhaust. Now I'm very upset bc I've spent alot of money hoping to have a perfect car and now I feel it's even worse off than before. Do you have any idea what's wrong with my explorer and also is there anyway that I can findout if the 1st mechanic did something to my truck on purpose since it wasn't running like this from the start? Thank you for any advice you can help me with. - Isaac