You mentioned only two hours post, and four hours post. How do you know two hours IS the peak?
With only two data points it looks as if you sugars are just going up from 5.8 to 7.7, which just tells me you didn't bolus correctly :/
Try again, but check before the meal, then every hour for 4-5 hours and see what you are getting. Sometimes i find if i inject too long before eating the insulin brings me down for the first hour and just shifts my peak, combined with high fat or protein meals i end up with my peak at 3 or 4 hours in and usually have to inject more to avoid sitting at the four hour reading.
2 numbers isn't really enough in my eyes to actually know where your peak is.
EDIT - Depends on the sweetner you are using, some do contain forms of sugar but in very small amounts and it MAY increase your levels if you use lots or are sensitive. If also MAY be that your basal rate is two low and your bolus brings you down but the basal cant hold you there. If you are on MDI its a bad situation because some people require multiple basal rates ie - higher in the day, and then low at night and as such they go high or low since they are only covering 1 of those needs instead of both.