Here are a few tips around selecting a new radio
1. For it to do everything you want then you probably need a 4 channel set. If you have an MFU then it is 4 channel minimum.
It is well worth sitting down and figuring out what you want the truck to do and then looking for the number of channels that will let you do that. If you have switched channels then 3 way switches are best - but with most sets there are ways to make 2 ways work. This is an important decision that will affect, enable and/or limit you in future. Please feel free to ask anyone on here for advice.
Most ground based car sets are 2 or 3 channel and will probably not do everything you want. That leaves marine and air sets. Now it gets a bit complex.
2. Air sets usually come as a "mode" set up. The modes are set as they are suited to different types of model. Some sets allow full switching between modes some do not. For Trucks Mode 2 is the most suitable. This is throttle on the left (up and down) and steering on the right (across). It does not necessarily matter so long as you can figure the channels but this is the most suitable set up.
3. Look at expansion options - i.e. the cost of a new RX and can the TX support (bind) to more than 1 TX. This means 1 tx many trucks. I use Spektrum as they have model match, others do not. Anyone having seen my models probably knows I can switch between them just by selecting on the TX, unselected models are "dead", Most other sets do not have this but its not that important so long as you turn it off.
4. Set up - Different models need different set ups. Most trucks need all the main fully proportional channels to auto zero. If it does not then you will need to fit a return spring set. For Spektrum they are free from Horizon - but the last one I had had no instructions.... Most sets have them in the box but ask.
5. For MFU1 set up you need to be able to stretch the channel movement. You can do this with the trim but some cheaper sets do not show you where this is. The best alternative is to use dual rates - the operation differs but someone here will be able to help. MFU3 is more forgiving but the MFU set up is more involved
6. Throttle can be vicious. The MFU reduces power when there is no trailer attached (5th wheel switch) as the weight is reduced and you need less. Most radios do not have dual rates on throttle so you need some way to emulate this. That is exponential. Some have just a percentage - others have curves. The curves are best but not essential.
1. Number of channels you need
2. Cost of extra RX's
3. TX Mode ( 2 is best but not essential)
4. Throttle zero return (spring set)
5. Dual rates
7. Mix capability (useful for combining outputs e.g. to give 3 way control when only 2 way switches are available, make another channel have secondary movement.
If in doubt ask.
FRsky, Spektrum, Futaba Flysky, Graupner