Problem with takeoff/landing roll

Here's what I have:
Dell Inspiron 5150
3.06 GHz Pentium 4
768 mb of RAM
64mb Nvidia GeForce FX Go5200
FPS at time of problem: 20-30 FPS.
I am using a Meljet 777-300ER in World Tour livery and whenever I go to JFK, EWR, HPN, MIA, TNCA (Aruba) and TNCM (St. Martin) and almost any airport, everytime I do a takeoff roll, from the point where airspeed becomes alive to say 150 knots, it goes very slow but my FPS remains high (doesn't go below 20 FPS and stays within 40 FPS) and the engine parameters shows it's still at full throttle, the view of the runway from the cockpit or in spot view, looks like it's speeding up, then around 70 knots it looks like it's going slow all of a sudden say like 20mph then when i wait and it reaches 110+ knots, after that I rotate and it lags again but the FPS shows fine performance, it returns to normal when I'm above 3 to 4,000 ft above ground. The same stuff happens on apporach and landing making it hard to gauge if it needs power boost before touchdown to maintain airspeed.
No matter what aircraft I use, it's the same problem. Even occurs with the LearJet 45, the 777-200ER, Beech starship, Cessna 172.
I even changed hardware display resolution, chagned texture size, details, effects and still the same problem.
It's like it's not the video performance but like the system or the program itself. It's hard to explain, other than this was the best I can come up with, it'd take a video to clearly show what I'm trying to explain.
Does anyone know what's the problem?
Dell Inspiron 5150
3.06 GHz Pentium 4
768 mb of RAM
64mb Nvidia GeForce FX Go5200
FPS at time of problem: 20-30 FPS.
I am using a Meljet 777-300ER in World Tour livery and whenever I go to JFK, EWR, HPN, MIA, TNCA (Aruba) and TNCM (St. Martin) and almost any airport, everytime I do a takeoff roll, from the point where airspeed becomes alive to say 150 knots, it goes very slow but my FPS remains high (doesn't go below 20 FPS and stays within 40 FPS) and the engine parameters shows it's still at full throttle, the view of the runway from the cockpit or in spot view, looks like it's speeding up, then around 70 knots it looks like it's going slow all of a sudden say like 20mph then when i wait and it reaches 110+ knots, after that I rotate and it lags again but the FPS shows fine performance, it returns to normal when I'm above 3 to 4,000 ft above ground. The same stuff happens on apporach and landing making it hard to gauge if it needs power boost before touchdown to maintain airspeed.
No matter what aircraft I use, it's the same problem. Even occurs with the LearJet 45, the 777-200ER, Beech starship, Cessna 172.
I even changed hardware display resolution, chagned texture size, details, effects and still the same problem.
It's like it's not the video performance but like the system or the program itself. It's hard to explain, other than this was the best I can come up with, it'd take a video to clearly show what I'm trying to explain.
Does anyone know what's the problem?