Hi I have a Volvo 1995 850 glt (non-turbo) and the engine can't go over 2000rmps under-load, but it can rev just fine in park or neutral. I tried putting it in sport and economy modes and shifting to different drive gears and nothing helped. It can get up to high way speeds (just takes longer). The OBD under the hood say nothing is wrong and there is no check engine on (and i know that works). The problem started one day randomly and at first it only happened when the engine got to running temperature (or it might have been running time) but now it's right off the bat.

 

Hmmm, clogged Cat?

 

Sorry I am new to these cars, when you say "clogged Cat" what do you mean?

 

clogged catalytic converter. The catalytic converter has a metalic grid which heats up and does some chemistry magic to reduce emissions. If your car has been in poor tune, carbon from the exhaust can build up on the grid restricting airflow through the exhaust system. A quick test is to remove the oxygen sensor (creating a vent hole) and see if anything changes. The other way airflow can be restricted is on the intake - check your air filter for any crud. After that, I'd start checking for other issues -

A check list (in my suggested order of discovery):

restricted air intake - check air filter, check intake air temp sensor (google this topic for ideas on how to test)
restricted exhaust - visually inspect outside, try the test for the clogged cat
bad sensors - check engine coolant temp sensor, check MAF (mass airflow sensor), check engine speed sensor
check spark - coil, wires, cap/rotor, plugs? I'd look at the date code on the wires to see how old and if over 5 years, do a "stage 0" tune up (complete kit, have the coil tested)
check fuel pressure (test at rail, could be possible restricted fuel filter or wonky pressure regulator)
check throttle/ switch connections

Hope this helps!