CLUTCH SLIPS, ENGINE SPEED INCREASES BUT ROAD SPEED DOES NOT INCREASE. WHAT COULD THE PROBLEM BE? HAVE JUST REPLACED THE CLUTCH PLATE, CLUTCH SLAVE CYLINDER AND THE PRESSURE PLATE. PRIOR TO THIS THE GEARS COULD NOT ENGAGE BUT THERE-AFTER THEY WERE ABLE TO.

stick shifts are my love. for over 50 years,
ok if the slave cycl released 100% does it? ( look and see it fully retracted)
the clutch is bad if it slips. (linkage /slave good)
no matter what car it is.
that is right warm clutches slip more hot.
a physics thing. (disk surfaces)
here is what can be bad. (all)
bad throw out bearing actual or it sticks from worn out pinon surfaces.
bad PP bad pressure plate, spring weak.
bad DISK , worn thin it hits brass rivets and SLIPS
oil on disk from bad seal front end of tranny
front of tranny pinion shaft a wreck, galled and rusted. and makes the throwout bearing stick and not release.
(all the above is moot, if slave is ok, and master cyc.
moot in the the transmission is now pulled and all above is discovered. and in truth all is just changed out 3 part klt.
done many even 4wd a 10 hour job on those.
first one done was 1964. by me and before that motorcycles and after too.
hint #2 (other) on manual linkage , no slave
the clutch free play must be kept to spec or 1/2" or clutch will slip ignored say for years.

maybe the original problem was the clutch master cylinder
it the compensating port is blocked , it holds the clutch pressure plate off and slips the clutch
not the problem then did the clutch fork( release lever go back in the right wat

check /replace clutch cable or replace master cylinder. If the clutch has not been replaced it may need a clutch kit as the indications are that the pressure plate is weak ( worn clutch plate or from overheated clutch)

usually a slipping clutch is a bad clutch
the acid test is to remove the slave
point car in safe direction ,
start car in gear, does it slip now?
yes, then the clutch is bad.
you do this test off road safely..
it can only be 2 things, think about it.
1: bad clutch 99%
2; a seized ,while extended slave.

You probably have a hydraulic clutch. A hydraulic clutch has both a master and a slave cylinder. The slave cylinder engages/disengages the clutch plate. You might be low on clutch fluid in the master cylinder, or the system may need to bled similar to bleeding brakes. Worst case is you need a new clutch, pressure plate, and throwout bearing. They should all be replaced when doing a clutch job.

You have a worn out slipping clutch, the biggest load and most slipping always takes place when you start out, as speed increases the clutch slips less and less. A defective slave or master will not cause these symptoms, the pedal will just go to the floor and not come back up or have a real spongy feel to it. Have any shop you want drive this to confirm my guess as to what you need being the clutch replaced.

could be pressure plate or clutch too thin, maybe in need of replacement.

If your car has a manual gear box thn the clutch plate may need replacing, if need be better to replace the pro-kit i.e clutch pressure plate , clutch plate and the relaese bearing.

sounds like it needs the clutch replaced. Anytime it slips, it's because it's lose enough material that the pressure plate can't keep enough tension on the clutch plate and the flywheel. Likely, it was slipping and overheated, causing it to smoke(and probably smelled like someone grinding metal with an angle grinder.) This needs a clutch change, throwout bearing, pilot bearing, and a flywheel surfacing. There is no adjustment for these; the play only increases until it slips.