Some of these articulation errors are normal for his age:
http://www.talkingchild.com/speechchart.html
The frenulum being snipped probably had no effect. Not being able to suck through a straw/latch/blowing might be a sign of low tone, which can affect speech. I would contact your home elementary school and ask to have him evaluated. Usually services are offered through the school during school hours, so you could always go for private ST if this doesn't work for your schedule.
Since he's understandable by most other people, is very good. (I'd hold back on trying to fix his tongue placement at this point and see where the evaluation/his own development takes you.)