I purchased a used 2000 Sundeck 210 that needed a lot of work. The previous owner purchased it from the original owner, who seemed to neglect the boat. Originally, the boat came from Savannah, GA and had 220 hours on it. The previous owner told me that when he purchased it, the engine block was cracked so he replaced it with a "Vortec 5.7 from a truck". To cut some of the story out, I purchased the boat, as it did run and crank, but idled rough and had timing issues. Upon farther investigation and many hours of work, I discovered the engine serial number plate on the block and it was a mercruiser marine plate and the serial number traced back to be a 1994 5.0 litre (original motor was a 5.0, EFI). 2 different marine mechanics "looked" at it, the first one adjusted the timing, did a few maintenance items, said they water tested it and I should be in good shape. When we took it to the water, we found that it wouldn't go in reverse without going dead. A new shifting cable later, took it back to the water and it wouldn't plane out. The 2nd mechanic, after 3 weeks, adjusted the timing in the water (don't know if they finished) got the boat to plane out, ran it up to 42-4300 rpm, said it lost oil pressure, said I needed to replace the motor. Being that the boat cranks smoothly, runs smoothly and planes out, has no knocks, makes no noises of any kind, I thought they didn't investigate very much and couldn't rely on their suggestion. They told me it acted like an auto engine, because the oil pressure dropped, however, it has a mercruiser badge on it that looks original, so it's hard to believe. I checked pressure with a mechanical guage myself and the engine held 50 lbs of pressure, no problems, so I replaced the sender unit, seems to be good now. We used the boat several times last summer and never had any problems cranking, running and seems to run smooth. The only issue is it seems to be VERY slow planing with only 2-3 people on board, including myself and not much gear at all. I didn't clock it, but it the acceleration had much to be desired and seemed like it was lacking greatly. Also, I ran it up to around 4,200 RPM (if memory serves me correctly) and clocked it at 33-34 mph on a gps with the trim all the way down. The speed doesn't match the rpm at all at any point of acceleration. It has a knock sensor that was very rusty and looked like it was in bad shape, so I replaced it just now. I also plan to replace the plugs and wires as I'm sure they are past due. Any other ideas of what could cause this? Could it need more timing adjustment? or the knock sensor (Sierra replacement) be the problem? It has the factory SS 14x19 prop, looks to be a decent condition, one edge slightly rough, but doesn't seem to be enough to affect it.