Long time I don't get here!

Long story short I need to make some improvements on a VERY old app I made to a customer. It's a big one and it's completely in AS2. I have made several other apps in AS3 (so I am aware of its advantages over AS2) but due to the nature of this one there is not any chance of remake it. So I have to stick with AS2 in this case.

This app deals with several server interactions (retrieves data from DB using ASPX) and I make all those interactions through querystring (GET method), so when data is loaded I just loop through it and load it into an array. There is so many time I did that so I don't remember a couple things:

1) Is this possible do it instead using POST in AS2?
2) Would it will speed up things? I mean looping through POST data is perceptibly faster than through GET?

I am asking it because recently I added a feature to this app and the customer complained that when he uses this feature it longs to much to execute. Well this feature includes interaction with server (data retrieval). When I tested it I realized that the interaction itself (connection, request and data arrival) is very fast and that the delay is occurring during the process of PARSE the data from the querystring received. By the way, it's not a BIG querystring, around 1-2K at most.

So I ask again: may it being caused due to the fact I am parsing GET data? Would be POST faster?