Add liquidity: Buy at the ASK and Sell at the BID with LMT. Your delay from a retail connection and software (what you see and what is reality) is probably off about 1.5 seconds minimum. Remember the action is round trip (.75 seconds per trip leg) and your reaction is at least .25 seconds.
It may be just a semantic thing, but usually adding liquidity is when your order sit on the book. Buy at the ask usually remove liquidity.
%% 00.80 or .90 slippage still sounds excessive\ not normal, even if its worst fills , semi liquid stuff. TQQQ sure could do that $1 slippage with market order\fast dropping market; but i would not call that normal+ do use market order exits on tqqq some. Could probably get worse slippage that that selling close to open., Slippage can be positive also.