Try turning off the SAS (the T key?) I find this creates more drag and slow me down as I tumble through the atmosphere like an out of control washing machine. You could also try deploying the chute lower down. I like to wait until I'm around 1500m, well below the re-entry burn and wind. Lastly, if this still isn't working, it may simply be a case of too much mass creating too much stress. Try adding more parachutes.