Low temps and too smoky food, sounds like an airflow issue getting to the fire or a closed off stack on your exhaust side. On smaller horizontals, you should probably run with your exhaust stack fully open and then use your air intakes on the firebox to adjust the temps. More air for hotter temps, less air for lower temps. With the over smoked meat, I would guess that you were getting a white smoke, which means poor combustion, due to lack of air (O2) getting to the fire. You really are looking for a thin, blue smoke. So thin that you feel you might not be smoking the meat at all, but you will be. Smoke at the start of the cook, once the meat reaches a certain IT, it will not absorb any more smoke. Lump is fine, I am not familiar with the brand you were using, but work on the airflow and you should be ok. Might even make a test run with no meat and 1 bag of your lump, exhaust open and intakes wide open and see what temps you can get with that set up. Once you learn your smoker, you'll be smoking up some goodies in no time.