i agree w/ AR about the anaerobic aspect. Also many of the gels on the market today are actually composed of a large chunk of complex carbs...so while they may be "quick" to take, they are not quick to enter your system b/c it takes a while to get the body to convert them to a digestible form of simple glucose.
Something else that could be happening is that there is a delayed emptying of your bowel (or rather into your bowel). So the gus you are eating are sitting in your stomach b/c your blood supply is being diverted to your muscles (more metabolically active b/c of the activity and the body says "not now stomach, I'm busy". After the run, the food is still there and stomach is still saying "do something with this stuff", and so your body lets the food empty into the GI system, and then the glucose from that 'hits' your system, causing the spike.
The other thing that could be happening is that your liver has been releasing glycogen into the blood stream to help combat a low BG (b/c of your activity, and it wants your body to have plenty of 'food' to eat at the muscles). When you stop running, your liver doesn't really get this signal, and (not knowing that your pancreas is broken so it can't release insulin to combat extra glycogen/glucose), it continues to release glycogen after the exercise has ended, causing a spike.
The first situation could be handled by not taking gus or other carbs within about 1 hour of getting done w/ exercise. This will vary from person to person, according to exercise intensity, duration, etc, so that's a vague starting point at best. However, continue to take water and/or electrolyte replacements, especially if it is hot.
The second situation could be mititgated some by sending a signal to the liver so it knows the activity is over and it can stop. I've done this in the past with a recovery shake. The large amount of fluid that enters the stomach helps to signal to the liver. Alternatively (for a more economical option w/o the protein shake stuff) is to drink a glass of milk...it's got a good carb/protein mix so it helps with recovery in a similar fashion as the protein shake, but at a much more wallet-friendly price.
In both of these cases, depending on what my ending BG is, I may bolus insulin (on top of my food bolus) to help combat this rise in BG that seems to happen (since again the pancreas is broken and can't do this, and the liver may not get the signal in a very timely fashion).