First, you have had bad training advice b/c your issue is classic and easy to fix.
Okay--having spent far too much of my life on a track I can tell you right now STRENGTH IS NOT YOUR PROBLEM--what you describe is simple: you have not done enough work above that your lactate threshold--its hitting you like a wall at 60m because of one thing--your VO2 max is too low--you need a specific training targeted at raising that threshold--NO GEAR WILL HELP WITH THIS--in fact, it will hurt.
Trust me--you describe a classic sign of bad coaching--and you will not get a good coach if he/she thinks you are/have done gear b/c they risk their livelihood by training you.
You are plenty big enough--more muscle will just hurt you.
If you can't get a trainer--a good one--go to you local college, talk to the track coach (most will offer you some advice as your problem is classic and easy to fix--easy to tell you how, hard work to fix).
If you live in a big city or certain endurance hubs, find a performance lab that has the best rep and spend your $$ there---they will do more in 3 hours than 5 years of training.
If that fails or you can't afford it, I will tell you in detail how to fix your issue by June--your speed is not the issue--it's your cardiovascular (and, I bet, there is a couple of diet issues b/c you are not clearing lactic acid fast enough). BUT if you do any gear I will not help.
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