You should be beating NL5 with no problems with a TAG strategy just the same as NL2, maybe with a lower win rate. If you're sticking to the starting hands charts it means you are leaking post flop. You're either folding too much, not folding when you should fold, cbetting and multiple barreling too much in the wrong situations or getting in trouble in 3 bet pots. You'll have to analyze this yourself. In general, avoid trouble and you'll be back to winning again. And yes, there are many more regs, most are very tightish, these are like 20 to 30% of the players and then there is a 10% of so of LAGs. The fish are pretty dispersed, with luck you have 1 fish a table, maybe 2 sometimes, it isn't crawling with fish like NL2. As a rule generally don't go allin without the nuts postflop and without AA preflop, unless you are up against a complete fish or very spewy players, but going allin without the nuts vs. regs you'll run into trips, flushes and straights just about every time with an overpair or even two pair. Get used to check calling to control the pot or even folding in some situations with overpair or top pair when villain clearly indicates he was picked something up. Good folds save money.