 The purposes of this study are to determine whether an experimental drug known as tadalafil can reduce symptoms of dyspepsia fullness after eating, inability to finish a regular meal, bloating, discomfort or pain in the upper abdomen, belching after meals, nausea, vomiting in diabetic patients, andor reduce the amount of time the stomach takes to empty the contents of a standard meal. The safety of tadalafil given once daily for 8 weeks in this population will also be studied. 