My guess is your coming in a little slow... Come on final with a bit of speed 170-180 kts, then touchdown around 130-140... 140 on final is a little slow... Also you could try 30 degrees of flap as opposed to full, usually works for me... Don't be afraid of her on final, its a machine, bring her in fast!
Uh, I usually fly 150kts from the marker inbound in a 747-400......140 knots does not sound unreasonable to me in the 737-800, at lighter weights I would bet the Vref is even slower than that (at really low weights, the Vref in the 727-200 was 112 knots, and we flew the final approach at Vref+10 knots).
The key to landing the big jets well is coordinating the power reduction with the roundout and flare. Do not pull any power off until you are very close to the runway. RW in the 727 and 737-200 I would hold the power on there until around 20 feet on the radar altimeter, at that point I would slowly pull the power off so as to arrive at idle power just as the mains touch down. Not much pitch change was required maybe a degree or two. In the 727 we would actually relax the back pressure right before touchdown as this resulted in a better landing.
Part of your descent rate on the glideslope is your speed. The faster you fly final, the higher the descent rate will be to maintain the 3 degree path. Don't be afraid of flying the big airplanes at what seem like slow speeds, this is how they were designed to fly and achieve the performance numbers that they have. I'll hunt around and see if I can find a speed table for the -800 somewhere, 170 to 180 inside the marker is asking for a long landing. If you want the best and shortest landing distances you have to be on speed from at a minimum 500' agl........
ATP, CFI, CFII & MEI, CL30, 727, 737-200, DC-9
FS9, Active Sky 6.5 w/ASG, FSPax