I have a 1988 4X4 pick up 4 cylinder. When i start to pull a hill the rpms go up and you can hear the engine revving up but the truch won't pick up speed. I thought the clutch might be slipping but I can set the parking brake and the clutch doesn't slip, I can also take off on a hill with no problem. It seems to be in 4th and 5th gears whne it happens. Anyone ever had this problem before and how can I fix it. Thanks.

check fuel delivery injector---do compression test -pull valve cover check valves and lash--rockers
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The engine and the Trans are in timing with each other from the factory...If the RPMs are revving up but the TRANS isn't keeping up with the Engine The problem sounds to be in the trans...Unless your calipers are sticking and holding you back....!?...A Throttle position Sensor can give you problems because It controls the throttle but normally if it is faulty it should run rough at any level....Same goes for the Idle Air Control valve....A fault in either of these components will produce abnormal RPMs and a rough running engine....Early signs of a clogged fuel filter will stall you while going up a hill also.....Of course the engine will get a temperature increase because it is being overworked....It may not be as hot as you think considering the gauge reading you described...You would have to use a handheld thermometer for a positive engine degree reading....However if it is evidently boiling hot and gauge reads normal it sounds like a faulty sensor in which case is a different problem....Make sure coolant is full to be safe......m..

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.

Ask a local mechanic here ,as they very rarely give problems ,now is this the three cylinder engine or the 4 as their is a difference as to trying to you some idea as the problem and stop revving the engine up as you WILL KNACKER IT UP

Code 300 means you have a random miss that is not serious enough to pick one cylinder. The computer measures RPM on each cylinder as the plug fires. So it is not that a cylinder is not firing but rather that it is not producing enough power.
Other causes are vac leaks and lack of fuel.

I would start by checking the fuel pressure.

Unfortunately yes, the torque converter has gone bad, and it is slipping. Increased rpm is due to the lack of friction in the turbine / torque converter, the equivalent of a burned out clutch in a manual transmission. Burnt smell is due to overworked, overheated transmission fluid. Turning off the engine, and letting the fluid cool down, will improve the situation for a few miles, until temp goes up again.

Chances are the engine isn't too bad off but the tranny will need a rebuild

This generally indicates a vaccumn leak, or sticking idle air control valve.

Does temp gauge go up when this happens ? When was fuel filter changed last? If not recently, I'd start there.