What chain rings do you have? 52/42? A possible upgrade, possibly inexpensive, possibly weight-saving, would be your crank. Look for a 53/39.
Next buy a 54 to replace the 53, and train, train, train until you can push that big gear 54x12. Then you'll pass people!
I have a 30 year old, Italian, steel bike, which I bought new. Back then I could only afford Ofmega components. I keep it for nostalgia, and I ride it once in a while, just for fun. It has agressive, criterium geometry - very squirrely. I keep the bar height and seat height the same as it was fit for me by the little old Italian guy in the little bike shop in Italy where I bought it (he called me "Lemond"), back when I was flexible and could hunch over that far. Now when I get on it, for the first time in a while, I feel like I'm doing a handstand. It was my first "racing" bike, and yet it fit so perfectly that within the first few rides I learned to handle it's super responsive steering and for years it was the most comfortable bike I've ever ridden. As I said, it's nostalgic. Anyway, over the years I have gently upgraded it to full Campagnolo, to build it into my 80's dream bike. I got my Campy crank, "NOS", on ebay for $25.
You're wise not to get caught in the marketing induced mindset that you have to spend a lot of money to have fun in triathlon. It aint so.