99ram 3500 a sudden loss of power around 60 or 70 mph more of a stoll speed does not drop unless going up hill i can mash the clutch and let the rpms fall and relese clutch to normal running ive replaced fuel filter and transfer pump

there is not enough specif details available to be able to be close to exact But I will give an example that you can compare
in a manual transmission with a diff ratio of 3.909 and in 5th gear the rpms for 79 mph is 3200 rpms
the difference between gears is around 250 rpms so if you try to correlate the differences if it was in 4th gear the rpms would be around 3750 rpms so I suspect that the over drive section of the transmission is not engaging ( assuming that it is auto transmission)
so to answer your question , I am saying that it is too high in rpms for that speed and I suspect that the od is not being engaged as the rpms at 80mph I would be looking at around 3200-3500 rpms depending on the diff ratio

Your transmission is not shifting make sure it is in D, if automatic

problems with speed sensor for transmission. Computer uses a speed signal to shift transmission through the gears. Without speed input, the computer doesn't know when to shift the transmission. Either the speed sensor is bad or wiring from the ECM to the speed sensor is bad. Usually 2 wires lead to the sensor. The sensor generates a AC voltage signal with higher speeds generating more voltage and frequency. The ECM (computer), looks at the signal to see how fast the vehicle is traveling.

That is a typical RPM at that speed for most 6-speed 4 cylinder engines. The reason for this is that they have a much lower power output at lower RPMs (due to lack of torque), and the engineers want for you to have SOME acceleration to get up little hills.

sounds pretty normal. what speed do you try out the passing gear? anything above 35-45 mph and it will feel like neutral. Passing gear is actually only 1st gear. When you press down the pedal, it forces the transmisson to shift into low gear.

check the timing cuoldbe wrong

I had a similiar problem on my 1999 Dodge Ram 1500 Conversion Van. It ended up being a partial collapse of the catalytic converter which didn't allow adequate exhaust. The problem only showed itself because I could not get over 55 mph going up a small hill.

You sould have recieved a "recall" notice in the mail about the cruise control for fire and failure issues. they are adding a fusable link where the cruise control harness connects to the brake master cylinder. if you have not had the recall performed yet you should SERIOUSLY consider getting it done, mainly so it doesnt catch fire, but "could" be the result of the failure you've been experiancing! btw, almost ALL Ford vehicles have been affected with the cruise control recall. hope this helps!

When the transmission jumps the extra RPM by 200 or 300 RPM. That's your Torque Converter Clutch lock up disengaging or it's slipping. Pull the transmission dip stick out and check the fluid level and condition of the fluid, look to see that it's not burning. If the fluid is not burning then it's the Torque converter clutch unlocking and the Throttle position Sensor may need to be readjusted, or if the transmission is still running off a TV cable. The TV cable may need to be adjusted and or the transmission filter may be dirty and needs to be changed. Take it to a transmission shop and explain to them what the transmission is doing. I'm not sure if your transmission is an 4L80 or a 4L80E. If it's the 4L80E the PCM and ECM control the lock up to your converter. If the PCM detects a problem with the transmission, it drops the transmission fluid pressure to the converter clutch. If it's a 4L80, it's controlled by the TV cable and vacuum lines to the transmission modulator. Regardless they can look in to this when they change the transmission fluid and filter. Recap: Have the Suburban's ECM scanned for any transmission DTC codes. Service the transmission if the fluid is dark in colour and burnt. Adjust any linkage to the transmission that is an issue to it's performance. Good luck and keep me posted, be glad to help.