If your 353 is lagging, then it is perhaps defective. I've been running for years at the slower baud rate and never had any sort of lag issues. What exactly are you seeing?
I have used a BU-353 for a long time... I took my pc out of my car for about a year, sold the car and left the 353 in there by accident. I got a new one and put n in my car a few days ago. The problem is that I cannot get this unit to keep the needed 38400 baud rate. The lag at 4800 is ridiculous and sirfdemo is only giving me a temporary solution - it will last for a day, but as son as I start the car in the morning, it's back to 4800.
How do I make the change a bit more permanent?
I am driving on the interstate, or a highway where the speed limit is 60mph, and I will pass a street, and then about 3 seconds later, the marker passes the street. It has mad me miss a turn before lol. But anyway, It was the exact same way with the first one too. At really low speeds, this baud rate is sufficient. But I've done some testing and found that the higher rate is much more accurate as speed increases compared to the 4800... The weird thing s that my old one held my changes that were made through sirfdemo.