Your descriptions suggest that your tongue movement may be impaired due to nerve injury. Going back to your dentist to have a posy op exam is advised.
Yes, it is normal to have speech differences when teeth are added (crowns, bridges, dentures) or removed, as is your case. As long as you don't have any other symptoms such as a stroke or palsy or something else medically related I think it is the tooth. Usually a back tooth won't cause a lisp but every is different. I'd get an implant in that spot if you can. If not, get a bridge.